To celebrate Batman’s 75th anniversary (2014), DC Comics has produced a poster for comic shops; it highlights his milestones.
The first stories of the first nine characters/elements (Batman, Commissioner James Gordon, Robin, Joker, Catwoman, Gotham, Batmobile, Scarecrow, Penguin) on this timeline were written by Bill Finger. The first nine. The first nine.
Of the next five:
- Bat-Signal—first appeared in a story credited to Jack Schiff
- Two-Face—Bill did write his first story but credits Bob with the concept (some sources say Two-Face was the only villain Bob came up with…and some say that is no surprise, on two levels)
- Alfred—some sources credit Bill for Alfred’s first story but some (I believe correctly) credit Don Cameron
- Batcave (originally “Bat Cave”)—this was introduced in stages (i.e. first as “underground hangers” by Bill in 1942, then in the 1943 Batman movie serial, then in a 1943 Batman comic strip written by Bill, and finally in the comics in a story credited to Don Cameron)
- Riddler—Bill wrote his first story and years later Julius Schwartz acknowledged this
In other words, Bill had a hand (or was the hand) in twelve of the first fourteen milestones. (And beyond, but it would take a while to tally them all...)