Neil Gaiman was asked to do a television series for the BBC. Lenny Henry helped, too. Unfortunately, they fiddled with it, and while the end result was good, it was not entirely true to Gaiman's vision. So he went home, and used his days off to write the story he wanted to tell. It was later adapted by Mike Carey and Glenn Fabry as a miniseries for Vertigo Comics. It was not well-liked. There's a movie coming out. It's been in Development Hell since the book was written, but someone may be digging it up...