Tommy-Joe was raised in the Okey Dokey swamps. When a meteor exploded into 6 fragments and broke the dimensional barrier to Earth C, one fragment hit Timmy-Joe Terrapin endowing him with the power to move at super speed. Finding other animals had also recieved super powers, Fastback joined the heroic group known as Captain Carrot and his amazing Zoo Crew. His shell is also durable to the point of being bulletproof (though his head and limbs are not). Unlike real turtles he can exit his shell for short periods. Unlike many DC speedsters, he cannot phase through solid objects - but most speedsters don't have bulletproof shells.
During DC's 'Convergence' event, he was performing recon when he became involved in Wally West's efforts to protect his adopted home of Gotham City. The human of Gotham were of course unfamiliar to Fastback but Wally's opponents, murderous Amazons, threatened innocent lives, so Fastback naturally helped him in his fight. They were assisted by Wally's children, who had powers of their own. Once the clear danger to innocent lives was neutralized, Fastback moved on to his own problems.