Batman Jr. (20 BC – Unknown) is the adopted son of the fictional comic-book hero named Batman. He resides in Gotham City, spending most of his time in the secluded confines of the Batcave. There, he, under the guidance of his father's tutelage, regularly immerses himself in the study of a multitude of varied intellectual, athletic, and artistic disciplines which include, but are not limited to, nunchuck combat, MacGyveresque weapons construction, classical guitar, Cajun cuisine, child psychology, rocks, and bat husbandry.

Batman Jr. began his life on an undetermined date in the year 20 BC, shortly after the "official" beginning of the Roman Empire in 31 BC, in Rome. He was born into a family of reputable and successful toga merchants and, as such, was able to devote much of his time in his youth to his considerable curiosity unbound by the constraints of a destitution that afflicted many at that time. It was with this curiosity sensibly focused by his innate ingenuity that he led himself to the discovery of the "Duck Duck Pip Pip" time-traveling mechanism, the phenomenon which he exploited in the construction of the "P-Device" in his sixth month that brought him to present-day Gotham City.

After having been orphaned in Gotham when the "P-Device" could not transport him back to his own time, he was found by a social worker who arranged for his adoption by billionaire Bruce Wayne. Ever since, Wayne has raised him as his own, instructing him in the ways of the arcane art of "Batmanism" with the hope that he would one day assume the mantle of crime-fighter when it came time for Batman, Sr., either to retire or die.

After repairing the "P-Device," Batman Jr. will travel to the Cretaceous period, where he lived out his final days with the dinosaurs. Currently, however, he still resides in Gotham.