Clearly "The Good Doctor" is from Mary Shelley's "Frankenstein", "The Count" from Bram Stoker's "Dracula" and the "The Great Detective" from Sir Arthur Conan Doyle's works.
"Jack" is a reference to Jack the Ripper.
What about:
- Crazy Jill, who is a witch
- Rastov (Rasputin, the "mad monk"? not sure)
- Morris and McCab (Burke and Hare perhaps?)
- Owen, who is a druid
- The vicar, who is not a good Christian
- Larry Talbot (the werewolf from the movie "The Wolf Man", whose name was actually Larry Talbot.)
In the book's dedication, Zelazny lists:
- Mary Shelley
- Edgar Allan Poe
- Bram Stoker
- Sir Arthur Conan Doyle
- H. P. Lovecraft
- Ray Bradbury
- Robert Bloch
- Albert Payson Terhune
- and the makers of a lot of old movies...
Perhaps the other characters are based on their works?