Crisis on Infinite Earths was one of those comic book crossover events that lived to its hype of changing the DC Universe as fans knew it, with fan-favorite worlds and characters dying in the fight for the fate of the DC Multiverse. Among the most prominent casualties was the Silver Age Flash Barry Allen, who sacrificed his life to stop the villainous Anti-Monitor from consuming all of reality and give his fellow heroes a fighting chance. One of the most iconic moments of the story, the death was recreated during the Arrowverse's recent adaptation of the crossover as a beloved television incarnation of the Scarlet Speedster paid the ultimate price to save reality.
Marv Wolfman and George Perez's classic story had the Anti-Monitor kidnap Barry Allen so he couldn't interfere with his plans. With a devastating wave of pure antimatter, the omnipotent antagonist is able to consume all but five Earths in the Multiverse. The villain's opposite, the Monitor, recruited heroes from the remaining worlds to construct towers to keep the antimatter at bay, effectively ending the Anti-Monitor's initial rampage. As the villain prepares an antimatter cannon to obliterate the surviving worlds, the Flash breaks free and destroys the antimatter cannon by racing quickly around it, dismantling it but being consumed himself by the Speed Force in the desperate effort. Barry's sacrifice gave the heroes the time they needed to rally and defeat the Anti-Monitor once and for all, with the remaining Earths merged together in the aftermath.
The most obvious consequence of Barry's sacrifice, beyond the Crisis, is that he would remain dead for over 20 years before returning for good at the start of the 2008 crossover event Final Crisis. Barry's protege Wally West, the original Kid-Flash, would inherit his mentor's mantle and defend Central and Keystone Cities as the Flash for the Post-Crisis Earth. Barry would appear sporadically from the Speed Force to help Wally before his full resurrection, most notably in the fight against Zoom and during the 2005 crossover event Infinite Crisis to help his grandson Bart battle Superboy-Prime. While much of the DCU's pre-Crisis history would be erased, Barry's would largely remain intact, with the heroes mourning his loss.
The Arrowverse television crossover event "Crisis on Infinite Earths" had the heroes discover that the Barry Allen from the 90s Flash television series, with John Wesley Shipp reprising his fan-favorite role, had similarly been kidnapped by the Anti-Monitor. The adaptation had the Barry Allen of Earth-90 forced to run constantly to power the Anti-Monitor's antimatter cannon. Freed by Cisco Ramon, the Barry of Earth-90 stops the main Arrowverse Barry from Earth-1 from sacrificing himself to destroy the cannon. Fulfilling the Monitor's prophecy of a Barry Allen giving their life to save the world during the Crisis, the Earth-90 Flash saves the day one last time by destroying the cannon at the expense of his own life.
For decades, Barry Allen's death was one of the few in the entire comic book medium that stuck to underscore the gravity of his heroic sacrifice. The Scarlet Speedster had saved the fate of five worlds with his ultimate race, going out in a blaze of glory that thwarted the Anti-Monitor's plans.
The death of the Flash was a sequence so iconic and celebrated that the Arrowverse included it in its own adaptation of the crossover event, giving the television story one of its more memorable scenes standing above a whole bevy of them. And while Barry is back in the land of the living in comic books, his past sacrifice remains of the most heroic moments in his entire superhero career.