n the comic books, Bart is the fourth person to hold the mantle of The Flash. Preceding him were Jay Garrick, his grandfather Barry Allen and his grandfather's nephew Wally West.
Bart Allen is born in the future, the grandson of Barry and Iris West-Allen. Suffering from a hyper-accelerated metabolism, Bart ages so fast that he appears to be twelve when he is chronologically and psychologically only two years old. Bart was raised in a virtual reality machine by his grandfather President Thaddeus Thawne that created a simulated world to keep pace with Bart's time scale. Iris freed Bart when she learned that wasn't helping him and sent back to the present where Wally West, the third Flash, tracked him down and make his hyper metabolism normal.
Bart eventually became Wally West's partner known as Impulse, Kid Flash, and then Flash.
Eric and Fran Russell (great-great grandparents)
Iris West-Allen (grandmother)
Henry and Nora Allen (great-great grandparents)
Barry Allen (grandfather)
Wally West (second cousin)
Malcolm Thawne (great uncle)
Thaddeus Thawne (grandfather)
Eobord Thawne (grandfather)
Don Allen (father)
Meloni Thawne (mother)
Dawn Allen (aunt)
Arrow (mentioned only when Capt. Lance confuses Barry for Bart)