he was the original Flash. In the comics, this would have been WWII-era. But the Golden Age ended in the late 1940s and superheroes were more or less forgotten. In 1956 the Flash was reintroduced, but it was not the same Flash. He had a different name (Barry Allen), costume, and background. In his very first appearance, he is seen reading a comic book about the Jay Garrick Flash which is what inspires him to take up the name "Flash" after his accident.
A couple of years later, while doing some super-speed tricks, Barry inadvertently transports himself to a parallel universe where he finds Keystone City which is the hometown of his childhood comic book hero, the Jay Garrick Flash. The person he used to think of as fiction actually existed in this parallel universe. And thus Earth-Two and the DC Multiverse is born. The idea is that there are an infinite number of universes that take up the same physical space, but are separated by vibrational frequencies.