There's even a novel (kindle only, I think, so I haven't read it) on the Mabuse phenomenon: 'The Strange Case Of Doctor Mabuse' by David Kalat, which seems to be quite good, according to the Amazon feedback. An essay on both books and films.

There's three full length novels (Docto Mabuse, the Gambler; Doctor Mabuse's Last Game; The Testament of Doctor Mabuse) and a novella (Doctor Mabuses Colony), all written by Norbert Jaques. Excellently written!