Bart Allen originally came from the 25th century as Barry Allens grandson. Assuming the identity of Impulse, Bart remained mysterious, trying not to connect himself with any of the flash family. After Flash (barry allen) was lost to the Speed Force, Wally West left being kid flash, and became The Flash as Barry's replacement, and Bart decided to use the oppurtunity to become Kid Flash.
After revealing himself as barry's Grandson, Wally and the rest of the Justice League decided to keep Bart as Kid Flash, and sent him to join the Titans. Wally became an important member of the Titans. After taking a shot gun blast to the leg by Titan's enemy Deathstroke, Wally gained the ability to heal himself at extreme speed. Bart was later murdered when Inertia manipulated the Rogues to kill him. Bart was later returned to life by a magic bolt during the Final Crisis.