Bill Finger was a writer, who provided many of the inspirational ideas to Bob Kane's outline of Batman that helped make Batman a success....like the cowl, cape, gloves, the blue/grey color scheme, and even the Bruce Wayne name!
Unfortunately, his penchant for research did not make Bill Finger a quick writer, nor did Bob Kane have him included on creator credits for Batman (only noting his contributions after Bill Finger had passed).
Robin, Joker, Catwoman, Riddler, Penguin and Two-Face, as well as the Batmobile, Batcave...
...and even naming Gotham City!
Golden Age Green Lantern, Wildcat, and creating Lana Lang in Superboy. Some of his last work on Batman was in World's Finest Comics, working with Superman (there he created Moon Man and Atom-Master, among others).