Marc Tyler Nobleman wrote Bill the Boy Wonder: The Secret Co-Creator of Batman, which came out a couple months back. The book is about Bill Finger, who was responsible for an awful lot of the Batman mythology, even though Batman (co-)creator Bob Kane was the only officially recognized creator. This is why they named the Bill Finger Award, honoring writers who didn’t get the credit/attention coming to them, after Finger.
Noble has some additional material about Finger on his blog. Chief among them, a copy of a letter from Bill Finger describing the only time he seems to have ever stood up to Bob Kane. With only two of Finger’s letters surviving (the other also being on that page), it’s amazing such a rare occurrence was one of them.
There’s a whole page of bits of research that didn’t make it into the book. Perhaps the most controversial (given Grant Morrison’s recent statements about the gayness of Batman) are Finger’s thoughts on whether or not Batman was gay:
I knew many homosexuals but I certainly didn’t think of Batman in those terms. I thought of it in terms of … Frank Merriwell and Dick Merriwell, his half-brother, who was the kid he was taking care of. … In America we always talk about the Western hero and the pioneer kind of man—the Davy Crockett types—as being loners. They’re never really. They always have a sidekick. … Certainly there’s no homosexual relationship.
And really, Finger was there from day one, so he ought to have a fairly definitive opinion.