The story of Bruce Wayne is long and packed full of one dark adventure after another, but a person -- even a fictional one -- can only live that life for so long. Bruce educated himself, trained intensely and armed himself to become Batman for virtually his entire adult life until he physically couldn't do it anymore. What was to become of Batman when Bruce Wayne grew too old? That's the question the 1999 animated series Batman Beyond sought to answer by introducing us to Terry McGinnis and the Gotham of 2039.
In the show, Bruce Wayne discovered how far he could push himself physically only after being forced to break one of his own rules in order to survive. That's why, in 2019, Wayne retired from being Gotham's Dark Knight.
The very first episode of Batman Beyond, "Rebirth" (written by Alan Burnett and Paul Dini), opens with one of Bruce Wayne's last daring rescues as Batman.
Bunny Vreeland, a wealthy debutante, is kidnapped by a gang looking to ransom her. Under the cover of darkness, Batman, wearing a state-of-the-art suit, enters the jet hangar where the gang is held up and begins to do what he used to do best: Thrash bad guys. When it looks like they've been taken care of, Bruce takes a labored breath before his heart problems are revealed. While he tries to untie the debutante, one last thug, wielding a crowbar, attacks Batman from behind. Bruce can't fight anymore and is violently beaten. It looks like the end of Batman, until the Dark Knight spots a gun just within reach. He grabs it, knowing that it's the only way to survive this fight, and aims it at the thug, who immediately backs away and runs straight into law enforcement. Horrified by his actions, Bruce vows never again to don the cowl.
But why is this event so important to the character of Terry McGinnis, who hadn't even been born when this occurred and would only become Batman 20 years later?
According to the events of the Justice League Unlimited episode "Epilogue" (written by Bruce Timm and Dwayne McDuffie), Amanda Waller did everything to ensure that there would be another Batman, going so far as to covertly rewrite Warren McGinnis' genetic code to match that of Bruce Wayne. There's no doubt that, even if Waller had kept Project Batman Beyond going, she would have failed to recreate the Dark Knight. She knew that, which is why she stopped after the assassin she hired confronted her. Batman and Bruce Wayne are simply too closely entwined.