He is one of the core members and he sticks around when Superman and Batman get pissed off and quit.

- The first Flash (Jay Garrick) was a charter member of the Justice Society of America, the first superhero team. - The second Flash (Barry Allen) was a charter member of the Justice League of America, the second superhero team. - it was revealed that Garrick and Allen existed on fictional parallel worlds. Their powers allowed them to cross the dimensional boundary between worlds, and the men became good friends. Flash of Two Worlds (The Flash vol.1 #123) was the first crossover in which a Golden Age character met a Silver Age character. Here the details: "Golden Age The Flash first appeared in the Golden Age Flash Comics #1 (Jan. 1940), from All-American Publications, one of three companies that would eventually merge to form DC Comics. Created by writer Gardner Fox and artist Harry Lampert, this Flash was Jay Garrick, a college student who gained his speed through the inhalation of hard water vapors (later retconned into heavy water vapors), and who wore a winged metal helmet reminiscent of the mythological Greek god Hermes. He is notable as the first super-speedster in comics, and one of the first to have a single super-power as opposed to multi-powered heroes such as Superman. Garrick was a popular character in the 1940s, supporting both Flash Comics and All-Flash Quarterly (later published bi-monthly as simply All-Flash); co-starring in Comic Cavalcade; and being a charter member of the Justice Society of America, the first superhero team, whose adventures ran in All Star Comics. With superheroes' post-war decline in popularity, Flash Comics was canceled with issue #104 (1949). The Justice Society's final Golden Age story ran in All Star Comics #57 (1951; the title itself continued, as All Star Western). - Silver Age In 1956, DC Comics successfully revived superheroes, ushering in what became known as the Silver Age of comic books. Rather than bringing back the same Golden Age heroes, as Atlas Comics, the 1950s precursor of Marvel Comics, unsuccessfully tried to do, DC reimagined them as new characters for the modern age. The Flash was the first revival, in the aptly named tryout comic book Showcase #4 (Oct. 1956). This new Flash was Barry Allen, a police scientist who gained super-speed when bathed by chemicals after a shelf of them was struck by lightning. He adopted the name The Flash after reading a comic book featuring the Golden Age Flash. After several more appearances in Showcase, Allen's character was given his own title, The Flash, the first issue of which was #105 (resuming where Flash Comics had left off). The Silver Age Flash proved popular enough that several other Golden Age heroes were revived in new incarnations. A new superhero team, the Justice League of America, was also created, with the Flash as a charter member. - "The Flashes of Two Worlds" The Flash also introduced a much-imitated plot device into superhero comics when it was revealed that Garrick and Allen existed on fictional parallel worlds. Their powers allowed them to cross the dimensional boundary between worlds, and the men became good friends. Flash of Two Worlds (The Flash vol.1 #123) was the first crossover in which a Golden Age character met a Silver Age character. Soon, there were crossovers between the entire Justice League and the Justice Society; their respective teams began an annual get-together which endured from the early 1960s until the mid-1980s." Source and further information: http://en.wikipedia.org/wiki/Flash_%28comics%29