The Flash's Ending Confirms a Shocking Villain Is the One to Beat Him
The Flash has defeated plenty of villains in his time-fighting crimes, but absolutely none of them can beat him.

The Flash is the fastest man in the DC universe, which, as one might expect, means he needs powerful and dangerous villains to fight. Whether it's Barry Allen or Wally West, the Scarlet Speedster has faced a psychopathic speedster or a telepathic gorilla, but one villain has barely beaten the Flash.
Possessing some of the most powerful powers in the DC universe, The Flash is able to travel faster than the speed of light, phase through solid objects, create violent winds through the movements of his hands, and even travel back in time or travel through dimensions. This absurd power means that The Flash also needs an army of absurd villains, and while characters like Batman or Superman usually fight their villains one-on-one, Flash often makes his villains team up just to fight him Evenly matched. The Flash's villain, The Rogues, is one of the greatest villains DC has to offer, and it's all because they're a group that needs to work together to defeat their individual heroes. But despite that, the only villains to get The Flash to hang his hood aren't Gorilla Grodd, Eobard Thorne, or even Rogue. that's a A man named Diogenes.
Readers can see the villain who ultimately bankrupted The Flash in Mark Wade and Craig Brasfield's Flash Annual #4. While trying to find the hero who will grow up to end the world, the character of Waverider gets a glimpse into possible futures for The Flash. Looking 14 years into the future, Waverider sees a Flash who has started a family, married a woman named Bonnie, and has a son named David. David even has the powers of the Flash, but can't use them because the family is under witness protection from the villain Diogenes. When a woman named Bonnie Blackmon reaches out to The Flash, he is drawn into the world's largest crime syndicate and eventually the Flash is forced to retire.
Diogenes Forced Flash To Give Up His Mantle

Diogenes is not a typical villain that The Flash fights, he is not someone with super speed, nor is he a wizard from the future. He was a simple man with simple powers, and he acquired complete knowledge of anyone he came into contact with. Include their needs and wants. Diogenes uses this to rise in the criminal underworld, befriend politicians or whoever he needs. It is this simple force that compels Wally West Retired as Flash. While Bonnie and Wally were able to send Diogenes to prison, he managed to run into Wally and Bonnie on the way to prison, which allowed him to murder Wally's mother and threaten Bonnie's life. With Diogenes privy to every aspect of their lives, Wally had no choice but to relinquish his identity as The Flash and accept witness protection. It goes to show that a man as heroic and powerful as Wally would give up anything to protect his family if they were thrown into the line of fire, which is exactly how a man with only useful powers can be a veritable destroyer of worlds Couldn't do it.
The Flash is one of the greatest heroes of all time, but even he can't be everywhere at the same time. While the Flash will do everything in his power to save everyone, when his family is attacked, the only thing he can do is give up on being a hero, which is how nobodies like Diogenes beat him.