Arsène Lupin
A gentleman-burglar whose disguises, deductions, and theatrical planning make him both criminal and detective.
Inspector Ganimard
Lupin's persistent police adversary, capable but repeatedly forced to play within Lupin's scripts.
Miss Nelly Underdown
A shipboard acquaintance whose judgment matters to Lupin even when she recognizes his identity.
Sherlock Holmes
Conan Doyle's detective, borrowed by Leblanc as Lupin's formidable English rival; only in later sequels did Leblanc rename him 'Herlock Sholmes.'
The recurring narrators and clients
Observers whose limited knowledge lets Lupin hide in plain sight and reveal the trick at the end.