Joseph Green and Jim Finch. Sleuths, Sidekicks and Stooges: An Annotated Bibliography of Detectives, Their Assistants and Their Rivals in Crime, Mystery and Adventure Fiction, 1795-1995. Scolar Press, 1997.
I can't believe this print source was ever written, published, or sold, and yet all three things happened. This is a book of ... how can I even explain it ... it's like if an obsessive-compulsive fan of detective fiction had endless money and time to create something like Casaubon's unfinished, doomed "Key to all Mythologies" in George Eliot's Middlemarch. Except this got finished and wasn't doomed!
The book has sections for detectives, authors, books, sidekicks, and stooges. The detectives get most of the book's real estate (pages 43 to 748). Each name is accompanied by a brief description, basic personal information (nationality, sex, type, and location), a list of "sidekicks" and "stooges" (i.e. adversaries), a short biography of the author who created the detective, and bibliographical information. The rest of the book is mostly cross-references, so if you know the name of the stooge you can get to the detective.
Why would anyone use this book in the age of Google? I don't think anyone would. Yet there's something wonderful in the fact that it exists, that Green and Finch actually got paid (presumably) to create this crazy thing. And it's still in print, with a price of $200! Its Amazon rank is about 6,400,000 at the moment, which may be the worst rank I've ever seen, not that I've made a study of such things.
Winner: detective fiction fan nerdliness.