December 21 is the 355th day of the year (356th in leap years) in the Gregorian calendar; 10 days remain until the end of the year.

• AD 69 – The Roman Senate declares Vespasian emperor of Rome, the last in the Year of the Four Emperors.^[1]
• 1124 – Pope Honorius II is consecrated, having been elected after the controversial dethroning of Pope Celestine II.^[2]
• 1140 – After a siege of several weeks, the city of Weinsberg and its castle surrender to Conrad III of Germany.^[3]
• 1237 – The city of Ryazan is sacked by the Mongol army of Batu Khan.^[4]
• 1361 – The Battle of Linuesa is fought in the context of the Spanish Reconquista between the forces of the Emirate of Granada and the combined army of the Kingdom of Castile and of Jaén resulting in a Castilian victory.
• 1598 – Battle of Curalaba: The revolting Mapuche, led by cacique Pelentaru, inflict a major defeat on Spanish troops in southern Chile.^[5]

• 1620 – Plymouth Colony: William Bradford and the Mayflower Pilgrims land near what is now known as Plymouth Rock in Plymouth, Massachusetts.
• 1826 – American settlers in Nacogdoches, Mexican Texas, declare their independence, starting the Fredonian Rebellion.
• 1832 – Egyptian–Ottoman War: Egyptian forces decisively defeat Ottoman troops at the Battle of Konya.
• 1844 – The Rochdale Society of Equitable Pioneers commences business at its cooperative in Rochdale, England, starting the Cooperative movement.
• 1861 – Medal of Honor: Public Resolution 82, containing a provision for a Navy Medal of Valor, is signed into law by President Abraham Lincoln.
• 1872 – Challenger expedition: HMS Challenger, commanded by Captain George Nares, sails from Portsmouth, England.
• 1879 – World premiere of Henrik Ibsen's A Doll's House at the Royal Theatre in Copenhagen, Denmark.
• 1883 – The Royal Canadian Dragoons and The Royal Canadian Regiment, the first Permanent Force cavalry and infantry regiments of the Canadian Army, are formed.
• 1891 – James Naismith, a Canadian-American gym teacher at Springfield College, publishes the first rules for the game now known as basketball and brings it to his class, which then plays the first game of basketball.^[6][7]

• 1907 – The Chilean Army commits a massacre of at least 2,000 striking saltpeter miners in Iquique, Chile.^[8]
• 1910 – An underground explosion at the Hulton Bank Colliery No. 3 Pit in Over Hulton, Westhoughton, England, kills 344 miners.
• 1913 – Arthur Wynne's "word-cross", the first crossword puzzle, is published in the New York World.
• 1919 – American anarchist Emma Goldman is deported to Russia.
• 1923 – United Kingdom and Nepal formally sign an agreement of friendship, called the Nepal–Britain Treaty of 1923, which superseded the Treaty of Sugauli signed in 1816.
• 1934 – Lieutenant Kijé, one of Sergei Prokofiev's best-known works, premiered.^[9]
• 1936 – First flight of the Junkers Ju 88 multi-role combat aircraft.
• 1937 – Snow White and the Seven Dwarfs, the world's first full-length animated feature, premieres at the Carthay Circle Theatre.
• 1941 – World War II: A Thai-Japanese Pact of Alliance is signed.
• 1946 – An 8.1 M_w earthquake and subsequent tsunami in Nankaidō, Japan, kills over 1,300 people and destroys over 38,000 homes.
• 1963 – "Bloody Christmas" begins in Cyprus, ultimately resulting in the displacement of 25,000–30,000 Turkish Cypriots and destruction of more than 100 villages.
• 1965 – International Convention on the Elimination of All Forms of Racial Discrimination is adopted.
• 1967 – Louis Washkansky, the first man to undergo a human-to-human heart transplant, dies in Cape Town, South Africa, having lived for 18 days after the transplant.
• 1968 – Apollo program: Apollo 8 is launched from the Kennedy Space Center, placing its crew on a lunar trajectory for the first visit to another celestial body by humans.
• 1970 – First flight of F-14 multi-role combat aircraft.
• 1973 – The Geneva Conference on the Arab–Israeli conflict opens.
• 1979 – Lancaster House Agreement: An independence agreement for Rhodesia is signed in London by Lord Carrington, Sir Ian Gilmour, Robert Mugabe, Joshua Nkomo, Bishop Abel Muzorewa and S.C. Mundawarara.
• 1988 – A bomb explodes on board Pan Am Flight 103 over Lockerbie, Dumfries and Galloway, Scotland, killing 270.^[10] This is to date the deadliest air disaster to occur on British soil.
• 1988 – The first flight of Antonov An-225 Mriya, the largest aircraft in the world.
• 1991 – Dissolution of the Soviet Union: The leaders of 11 now effectively autonomous Soviet republics sign the Alma-Ata Protocol establishing the Commonwealth of Independent States in place of the collapsing Soviet Union.^[11]
• 1992 – A Dutch DC-10, flight Martinair MP 495, crashes at Faro Airport, killing 56.
• 1995 – The city of Bethlehem passes from Israeli to Palestinian control.
• 1999 – The Spanish Civil Guard intercepts a van loaded with 950 kg of explosives that ETA intended to use to blow up Torre Picasso in Madrid, Spain.
• 1999 – Cubana de Aviación Flight 1216 overshoots the runway at La Aurora International Airport, killing 18.^[12]
• 2004 – Iraq War: A suicide bomber kills 22 at the forward operating base next to the main U.S. military airfield at Mosul, Iraq, the single deadliest suicide attack on American soldiers in Iraq.
• 2012 – 2012 phenomenon: Festivities are held in parts of Mesoamerica to commemorate the conclusion of b’ak’tun 13, a roughly 5,126-year-long cycle in the Mesoamerican Long Count Calendar whose passing many New Age spiritualists had earlier held to portend a variety of cataclysmic or transformative events.^[13]
• 2020 – A great conjunction of Jupiter and Saturn occurs, with the two planets separated in the sky by 0.1 degrees. This is the closest conjunction between the two planets since 1623.^[14]
• 2023 – Fourteen people are killed and 25 others injured during a mass shooting at Charles University in Prague, Czech Republic. The perpetrator, a student at the university, kills himself after police arrived; he also killed his father before the shooting.^[15]

• 968 – Minamoto no Yorinobu, Japanese samurai (d. 1048)
• 1401 – Masaccio, Italian painter (d. 1428)^[16]
• 1468 – William Conyers, 1st Baron Conyers, English baron (d. 1524)
• 1505 – Thomas Wriothesley, 1st Earl of Southampton, English politician (d. 1550)^[17]
• 1538 – Luigi d'Este, Catholic cardinal (d. 1586)
• 1542 – Thomas Allen, English mathematician and astrologer (d. 1632)
• 1550 – Man Singh I, Mughal noble (d. 1614)^[18]
• 1596 – Peter Mohyla, Ruthenian Orthodox metropolitan and saint (d. 1646)

• 1603 – Roger Williams, English minister, theologian, and politician, 9th President of the Colony of Rhode Island (d. 1684)
• 1615 – Benedict Arnold, Rhode Island colonial governor (d. 1678)^[19]
• 1672 – Benjamin Schmolck, German pastor and composer (d. 1737)
• 1714 – John Bradstreet, Canadian-English general (d. 1774)
• 1728 – Hermann Raupach, German harpsichord player and composer (d. 1778)
• 1778 – Anders Sandøe Ørsted, Danish jurist and politician, 3rd Prime Minister of Denmark (d. 1860)
• 1795 – Jack Russell, English priest, hunter, and dog breeder (d. 1883)
• 1795 – Leopold von Ranke, German historian, author, and academic (d. 1886)^[20]
• 1803 – Achille Vianelli, Italian painter and academic (d. 1894)
• 1804 – Benjamin Disraeli, English lawyer and politician, Prime Minister of the United Kingdom (d. 1881)^[21]
• 1805 – Thomas Graham, Scottish chemist and academic (d. 1869)
• 1811 – Archibald Tait, Scottish-English archbishop (d. 1882)
• 1815 – Thomas Couture, French painter and educator (d. 1879)
• 1820 – William H. Osborn, American businessman (d. 1894)
• 1830 – Bartolomé Masó, Cuban soldier and politician (d. 1907)
• 1832 – John H. Ketcham, American general and politician (d. 1906)
• 1840 – Ernest de Munck, Belgian cellist and composer^[22] (d. 1915)^[23]
• 1840 – Namık Kemal, Turkish journalist, playwright, and activist (d. 1888)
• 1843 – Thomas Bracken, Irish-New Zealander journalist, poet, and politician (d. 1898)
• 1850 – Zdeněk Fibich, Czech composer and poet (d. 1900)
• 1851 – Thomas Chipman McRae, American lawyer and politician, 26th Governor of Arkansas (d. 1929)
• 1857 – Joseph Carruthers, Australian politician, 16th Premier of New South Wales (d. 1932)
• 1859 – Gustave Kahn, French poet and critic (d. 1936)
• 1866 – Maud Gonne, Irish nationalist and political activist (d. 1953)^[24]
• 1868 – George W. Fuller, American chemist and engineer (d. 1934)
• 1872 – Trevor Kincaid, Canadian-American zoologist and academic (d. 1970)
• 1872 – Lorenzo Perosi, Italian priest and composer (d. 1956)
• 1872 – Albert Payson Terhune, American journalist and author (d. 1942)
• 1876 – Jack Lang, Australian lawyer and politician, 23rd Premier of New South Wales (d. 1975)
• 1877 – Jaan Sarv, Estonian mathematician and scholar (d. 1954)
• 1878 – Jan Łukasiewicz, Polish-Irish mathematician and philosopher (d. 1956)
• 1884 – María Cadilla, Puerto Rican writer, educator, women's rights activist (d. 1951)^[25]
• 1885 – Frank Patrick, Canadian ice hockey player and coach (d. 1960)
• 1888 – Jean Bouin, French runner and rugby player (d. 1914)
• 1889 – Sewall Wright, American geneticist and biologist (d. 1988)
• 1890 – Hermann Joseph Muller, American geneticist and biologist, Nobel Prize laureate (d. 1967)
• 1891 – John William McCormack, American lawyer and politician, 53rd Speaker of the United States House of Representatives (d. 1980)
• 1892 – Walter Hagen, American golfer (d. 1969)
• 1892 – Rebecca West, English journalist and author (d. 1983)
• 1896 – Konstantin Rokossovsky, Marshal of the Soviet Union during World War II (d. 1968)
• 1900 – Luis Arturo González López, Guatemalan supreme court judge and briefly acting president (d. 1965)

• 1905 – Käte Fenchel, German mathematician (d. 1983)^[26]
• 1905 – Anthony Powell, English author (d. 2000)^[27]
• 1909 – Seichō Matsumoto, Japanese journalist and author (d. 1992)
• 1911 – Josh Gibson, American baseball player (d. 1947)^[28]
• 1913 – Arnold Friberg, American illustrator and painter (d. 2010)
• 1914 – Frank Fenner, Australian microbiologist and virologist (d. 2010)
• 1917 – Heinrich Böll, German novelist and short story writer, Nobel Prize laureate (d. 1985)
• 1918 – Donald Regan, American colonel and politician, 11th White House Chief of Staff (d. 2003)
• 1918 – Kurt Waldheim, Austrian colonel and politician; 9th President of Austria (d. 2007)^[29]
• 1919 – Doug Young, American voice actor (d. 2018)
• 1920 – Alicia Alonso, Cuban ballerina and choreographer, founded the Cuban National Ballet (d. 2019)
• 1920 – Adele Goldstine, American computer programmer (d. 1964)^[30]
• 1922 – Itubwa Amram, Nauruan pastor and politician (d. 1989)
• 1922 – Cécile DeWitt-Morette, French mathematician and physicist (d. 2017)^[31]
• 1922 – Paul Winchell, American actor, voice artist, and ventriloquist (d. 2005)
• 1923 – Wat Misaka, American basketball player (d. 2019)^[32]
• 1926 – Arnošt Lustig, Czech author and playwright (d. 2011)
• 1926 – Joe Paterno, American football player and coach (d. 2012)^[28]
• 1930 – Phil Roman, American animator^[33]
• 1932 – U. R. Ananthamurthy, Indian author, poet, and critic (d. 2014)
• 1932 – Edward Hoagland, American author and critic
• 1933 – Jackie Hendriks, Jamaican cricketer
• 1933 – Robert Worcester, American businessman and academic, founded MORI
• 1934 – Giuseppina Leone, Italian sprinter
• 1934 – Hanif Mohammad, Pakistani cricketer (d. 2016)
• 1935 – John G. Avildsen, American director, producer, and cinematographer (d. 2017)
• 1935 – Lorenzo Bandini, Italian racing driver (d. 1967)
• 1935 – Phil Donahue, American talk show host and producer^[34] (d. 2024)^[35]
• 1935 – Stela Popescu, Romanian actress (d. 2017)
• 1935 – Edward Schreyer, Canadian academic and politician, Governor General of Canada^[36]
• 1937 – Jane Fonda, American actress and activist^[37]
• 1938 – Larry Bryggman, American actor^[34]
• 1939 – Lloyd Axworthy, Canadian academic and politician, 2nd Canadian Minister of Foreign Affairs
• 1939 – Wafic Saïd, Syrian-Saudi Arabian financier, businessman and philanthropist
• 1940 – Frank Zappa, American singer-songwriter, guitarist, composer and producer (d. 1993)^[28]
• 1942 – Hu Jintao, Chinese engineer and politician, 5th Paramount leader of China^[28]
• 1942 – Carla Thomas, American singer^[34]
• 1943 – Albert Lee, English guitarist and songwriter^[34]
• 1943 – Walter Spanghero, French rugby player
• 1944 – Michael Tilson Thomas, American pianist, composer, and conductor
• 1944 – Zheng Xiaoyu, Chinese diplomat (d. 2007)
• 1945 – Doug Walters, Australian cricketer
• 1946 – Roy Karch, American director, producer, and screenwriter
• 1946 – Carl Wilson, American singer-songwriter and guitarist (d. 1998)^[28]
• 1947 – Paco de Lucía, Spanish guitarist, songwriter, and producer (d. 2014)
• 1948 – Barry Gordon, American actor and voice artist; longest-serving president of the Screen Actors Guild (1988–95)
• 1948 – Samuel L. Jackson, American actor and producer^[34]
• 1948 – Dave Kingman, American baseball player
• 1949 – Thomas Sankara, Burkinabé captain and politician, 5th President of Burkina Faso (d. 1987)
• 1949 – Nikolaos Sifounakis, Greek lawyer and politician
• 1950 – Jeffrey Katzenberg, American screenwriter and producer, co-founded DreamWorks Animation^[28]
• 1950 – Max Maven, American magician and mentalist (d. 2022)
• 1950 – Lillebjørn Nilsen, Norwegian singer-songwriter and guitarist (d. 2024)
• 1951 – Steve Perryman, English footballer and manager
• 1952 – Joaquín Andújar, Dominican baseball player (d. 2015)
• 1952 – Dennis Boutsikaris, American actor^[34]
• 1952 – Steve Furniss, American swimmer
• 1953 – András Schiff, Hungarian-English pianist and conductor
• 1953 – Betty Wright, American singer-songwriter (d. 2020)^[38]
• 1954 – Chris Evert, American tennis player and coach^[39]
• 1955 – Jane Kaczmarek, American actress^[34]
• 1955 – Kazuyuki Sekiguchi, Japanese singer-songwriter and bass player
• 1956 – Dave Laut, American shot putter (d. 2009)
• 1957 – Ray Romano, American actor, producer, and screenwriter^[34]
• 1957 – Tony Lewis, English singer and songwriter (d. 2020)^[40]
• 1958 – Tamara Bykova, Russian high jumper
• 1959 – Florence Griffith Joyner, American sprinter and actress (d. 1998)^[28]
• 1959 – Krishnamachari Srikkanth, Indian cricketer
• 1960 – Sherry Rehman, Pakistani journalist, politician, and diplomat, 25th Pakistan Ambassador to the United States
• 1961 – Ryuji Sasai, Japanese bass player and composer
• 1963 – Govinda, Indian actor, singer, and politician
• 1964 – Kunihiko Ikuhara, Japanese director and illustrator
• 1964 – Joe Kocur, Canadian ice hockey player and coach
• 1965 – Glenn Coleman, Australian rugby league player
• 1965 – Andy Dick, American actor and comedian^[41]
• 1965 – Anke Engelke, Canadian-German actress, director, and screenwriter
• 1966 – Michelle Hurd, American actress^[34]
• 1966 – William Ruto, 5th President of Kenya^[28]
• 1966 – Kiefer Sutherland, British-Canadian actor, director, and producer^[42]
• 1967 – Terry Mills, American basketball player and coach
• 1967 – Mikheil Saakashvili, Georgian lawyer and politician, 3rd President of Georgia^[43]
• 1969 – Julie Delpy, French model, actress, director, and screenwriter^[34]
• 1969 – Mihails Zemļinskis, Latvian footballer, coach, and manager
• 1971 – Matthieu Chedid, French singer-songwriter and guitarist
• 1971 – Natalie Grant, American singer-songwriter and author^[34]
• 1972 – Y. S. Jaganmohan Reddy, Indian Politician, 17th Chief Minister of Andhra Pradesh
• 1973 – Irakli Alasania, Georgian colonel and politician, Georgian Minister of Defense
• 1973 – Matías Almeyda, Argentine footballer and manager
• 1974 – Karrie Webb, Australian golfer
• 1975 – Paloma Herrera, Argentine ballerina
• 1977 – Buddy Carlyle, American baseball player^[44]
• 1977 – Corey Collymore, Barbadian cricketer^[45]
• 1977 – Leon MacDonald, New Zealand rugby player
• 1977 – Emmanuel Macron, French politician, 25th President of France^[46]
• 1977 – Freddy Sanchez, American baseball player^[47]
• 1978 – Emiliano Brembilla, Italian swimmer
• 1978 – Charles Dera, American pornographic actor, dancer, model, and mixed martial arts fighter
• 1978 – Shaun Morgan, South African musician, singer, and guitarist
• 1978 – Rutina Wesley, American actress^[34]
• 1979 – Steve Montador, Canadian ice hockey player (d. 2015)
• 1981 – Marta Fernández, Spanish basketball player^[48]
• 1981 – Cristian Zaccardo, Italian footballer
• 1982 – Primo Colón, Puerto Rican wrestler^[49]
• 1982 – Philip Humber, American baseball player
• 1982 – Tom Payne, English actor^[28]
• 1983 – Taylor Teagarden, American baseball player^[50]
• 1983 – Steven Yeun, American actor^[34]
• 1985 – Tom Sturridge, English actor
• 1987 – Khris Davis, American baseball player^[51]
• 1988 – Danny Duffy, American baseball player^[52]
• 1988 – Perri Shakes-Drayton, English sprinter and hurdler
• 1989 – Mark Ingram II, American football player^[53]
• 1989 – Tamannaah, Indian actress
• 1991 – Nic Maddinson, Australian cricketer^[54]
• 1991 – Otis, American wrestler^[55]
• 1991 – Riccardo Saponara, Italian footballer
• 1992 – Ha Ha Clinton-Dix, American football player^[56]
• 1992 – Jamie Oleksiak, Canadian ice hockey player^[57]
• 1994 – Luke Brooks, Australian rugby league player^[58]
• 1996 – Ben Chilwell, English footballer^[59]
• 1996 – Kaitlyn Dever, American actress^[34]
• 1997 – Madelyn Cline, American actress and model^[28]
• 1997 – Charlie McAvoy, American ice hockey player ^[60]
• 2002 – Clara Tauson, Danish tennis player^[61]
• 2006 – Cooper Flagg, American basketball player^[62]

• AD 72 – Thomas the Apostle, Roman martyr and saint (b. 1 AD)
• 882 – Hincmar, French archbishop and historian (b. 806)
• 956 – Sun Sheng, Chinese chancellor
• 975 – Al-Mu'izz, Fatimid caliph (b. 932)
• 1001 – Hugh of Tuscany, Italian margrave (b. 950)
• 1215 – Ali ibn Muhammad ibn al-Walid, Dāʿī al-Muṭlaq of Tayyibi Isma'ilism (b. c. 1128)^[63]
• 1308 – Henry I, Landgrave of Hesse (b. 1244)
• 1338 – Thomas Hemenhale, bishop of Worcester
• 1362 – Constantine III, king of Armenia (b. 1313)
• 1375 – Giovanni Boccaccio, Italian author and poet (b. 1313)
• 1504 – Berthold von Henneberg, German archbishop (b. 1442)
• 1536 – John Seymour, English courtier (b. 1474)
• 1549 – Marguerite de Navarre, queen of Henry II of Navarre (b. 1492)
• 1581 – Jean de la Cassière, 51st Grandmaster of the Knights Hospitaller (b. 1502)
• 1597 – Peter Canisius, Dutch priest and saint (b. 1521)

• 1608 – William Davison, secretary to Queen Elizabeth I of England (b. c. 1541)
• 1610 – Catherine Vasa, Swedish princess (b. 1539)
• 1701 – Sir Hugh Paterson, Baronet of Bannockburn (b. 1659)
• 1807 – John Newton, English soldier and minister (b. 1725)
• 1824 – James Parkinson, English physician and paleontologist (b. 1755)
• 1869 – Friedrich Ernst Scheller, German jurist and politician (b. 1791)
• 1873 – Francis Garnier, French admiral and explorer (b. 1839)
• 1889 – Friedrich August von Quenstedt, German geologist and palaeontologist (b. 1809)

• 1920 – Mohammed Abdullah Hassan, leader of the Dervish movement (b. 1856)
• 1929 – I. L. Patterson, American politician, 18th Governor of Oregon (b. 1859)
• 1933 – Knud Rasmussen, Greenlandic anthropologist and explorer (b. 1879)
• 1935 – Ted Birnie, English footballer and manager (b. 1878)
• 1935 – Kurt Tucholsky, German-Swedish journalist and author (b. 1890)
• 1937 – Violette Neatley Anderson, American judge (b. 1882)^[64]
• 1937 – Ted Healy, American comedian and actor (b. 1896)
• 1937 – Frank B. Kellogg, American lawyer and politician, 45th United States Secretary of State, Nobel Prize laureate (b. 1856)
• 1940 – F. Scott Fitzgerald, American novelist and short story writer (b. 1896)
• 1945 – George S. Patton, American general (b. 1885)
• 1948 – Władysław Witwicki, Polish psychologist, philosopher, translator, historian (of philosophy and art) and artist (b. 1878)^[65]
• 1952 – Kenneth Edwards, American golfer (b. 1886)
• 1953 – Kaarlo Koskelo, Finnish-American wrestler and businessman (b. 1888)
• 1957 – Eric Coates, English viola player and composer (b. 1886)
• 1958 – H.B. Warner, English actor (b. 1875)
• 1958 – Lion Feuchtwanger, German-American author and playwright (b. 1884)
• 1959 – Rosanjin, Japanese calligrapher, engraver, and painter (b. 1883)
• 1963 – Jack Hobbs, English cricketer and journalist (b. 1882)
• 1964 – Carl Van Vechten, American author and photographer (b. 1880)^[66]
• 1965 – Claude Champagne, Canadian violinist, pianist, and composer (b. 1891)
• 1968 – Vittorio Pozzo, Italian footballer, coach, and manager (b. 1886)
• 1974 – Richard Long, American actor and director (b. 1927)
• 1982 – Abu Al-Asar Hafeez Jullundhri, Pakistani poet and composer (b. 1900)
• 1983 – Paul de Man, Belgian-born philosopher, literary critic and theorist (b. 1919)
• 1988 – Nikolaas Tinbergen, Dutch-English ethologist and ornithologist, Nobel Prize laureate (b. 1907)
• 1992 – Stella Adler, American actress and educator (b. 1901)^[67]
• 1992 – Albert King, American singer-songwriter, guitarist, and producer (b. 1924)
• 1992 – Nathan Milstein, Russian-American violinist and composer (b. 1903)
• 1998 – Ernst-Günther Schenck, German colonel and physician (b. 1904)
• 2004 – Autar Singh Paintal, Indian physiologist and neurologist (b. 1925)
• 2006 – Saparmurat Niyazov, Turkmen engineer and politician, 1st President of Turkmenistan (b. 1940)
• 2009 – Edwin G. Krebs, American biochemist and academic, Nobel Prize laureate (b. 1918)
• 2009 – Christos Lambrakis, Greek journalist and businessman (b. 1934)
• 2010 – Enzo Bearzot, Italian footballer and manager (b. 1927)
• 2013 – Edgar Bronfman Sr., Canadian-American businessman and philanthropist (b. 1929)
• 2013 – John Eisenhower, American historian, general, and diplomat, 45th United States Ambassador to Belgium (b. 1922)
• 2014 – Udo Jürgens, Austrian-Swiss singer-songwriter and pianist (b. 1934)
• 2014 – Sitor Situmorang, Indonesian poet and author (b. 1923)
• 2014 – Billie Whitelaw, English actress (b. 1932)^[68]
• 2017 – Bruce McCandless II, US astronaut who conducted the first untethered spacewalk (b. 1937)
• 2019 – Andrew Clennel Palmer, British engineer (b. 1938)^[69]
• 2024 – Michelle Botes, South African actress (b. 1962)^[70]
• 2024 – Art Evans, American actor (b. 1942)^[71]

• Armed Forces Day (Philippines)
• Christian feast day:
  • O Oriens
  • Peter Canisius
  • Thomas the Apostle
  • December 21 (Eastern Orthodox liturgics)
• Forefathers' Day (Plymouth, Massachusetts)
• São Tomé Day (São Tomé and Príncipe)

Wikimedia Commons has media related to December 21.

• BBC: On This Day
• The New York Times: On This Day
• Historical Events on December 21