The story goes that Vince Sullivan, editor at DC was looking for a feature that might duplicate the success of Superman, and when Bob Kane stopped in to drop off some of his gag strips Sullivan mentioned it to him.
Kane went back to his studio and since his stye was more suited to humor than adventure he traced over some Alex Raymond Flash Gordon comic strips and developed a look for a character called Bat Man.
Kane needed some stories to illustrate so he called on Bill Finger to work with him. Finger didn't care for the bright red character Kane had developed and suggested a bat shaped cape and cowl rather than the rigid wings and domino style mask Kane had.
Finger had always envisioned writing for the pulp magazines and was a big fan of Street and Smith's popular THE SHADOW magazine, borrowing extenstively from one of the Shadow stories Finger wrote THE CASE OF THE CHEMICAL SYNDICATE which DC bought and published in Detective Comics #27 with a May 1939 cover date.
Kane had his business savy father look over the agreement DC offered him, which was much the same one offered to the Superman team, and negotiated a deal which allowed him credit and creative control over the strip-- even if Kane himself had the work produced by a number of ghost artists-- including Jerry Robinson, Dick Sprang and Lew Schwartz. Kane often forgot to mention his collaborators when discussing Batman's success in later interviews, and sadly Bill Finger died a very poor man.
Kane acted as film consultant on Tim Burton's 1989 big budget version of the character starring Michael Keaton, and he passed away in 1998.