In 1939 Batman was created in an effort to capitalize on the popularity of the recently introduced Superman character.
Bob Kane did originate the idea of Batman, but what most people don't know is the character Kane created was vastly different than the character we call Batman today. His original vision much more closely resembled the look of Superman with red tights, a small mask, no gloves or gauntlets, and wings on the costume. Kane asked comic writer Bill Finger to take a look at his sketches. Finger suggested removing the red color from the costume, swapping the small mask for a cowl, adding a cape in place of the wings, and giving him gloves so he wouldn't leave behind fingerprints. Finger also came up with the name Bruce Wayne for Batman's secret identity. In addition to helping form the character of Batman, Finger also greatly contributed to many of Batman's allies and enemies as well as other aspects of the Batman universe.
Without including Bill Finger, Bob Kane presented the character of Batman to editor Vin Sullivan. Sullivan loved the character and he and Kane negotiated a deal, completely excluding Finger and leaving him without proper credit or compensation for his contributions. Several decades later in his autobiography, Bob Kane said Finger was "a contributing force on Batman right from the beginning".
Unfortunately, Bill Finger never received the real recognition or credit he deserved before he died in 1974. More recently his Granddaughter successfully challenged Warner Brothers to give her grandfather credit as a co-creator of Batman. In October of 2015, the comics Batman and Robin Eternal #3 and Batman: Arkham Knight Genesis #3 were the first to carry the updated credit "Batman created by Bob Kane with Bill Finger". In 2016 Batman v Superman: Dawn of Justice was the first film to give credit to Finger, and beginning with its second season the television series Gotham now also credits him.
While we can't change the past, we can now at least give proper credit to the man who was so vital to the creation of the character of Batman as we all know him.