Professor Zoom
As first conceived by writers, Bart was born in the 30th century to Meloni Thawne and Don Allen, and is part of a complex family tree of superheroes and supervillains. His father, Don, is one of the Tornado Twins and his paternal grandfather is Barry Allen, the second Flash. His paternal grandmother, Iris West Allen, is also the adoptive aunt of the third Flash, Wally West (Bart's first cousin once removed). Additionally, Bart is the first cousin of XS, a Legionnaire and daughter of Dawn Allen. On his mother's side, he is a descendant of supervillains Professor Zoom and Cobalt Blue as well as the half-brother of Owen Mercer, the second Captain Boomerang. In addition to these relatives, he had a supervillain clone known as Inertia.