There are quite a few theories attempting to link Fantômas and his extended family to other literary characters.
- Rocambole was the protagonist of a series of crime thriller novels, which lasted from 1857 to 1870. Rocambole started out as a villain, "a ruthless, brilliant schemer, motivated purely by greed. He steals and murders without remorse, but with a wicked sense of humor and banter". Then he redeemed himself, using his skills as a vigilante crime-fighter. Though always evading the law. His early death left two sons orphan. Two orphans that would inherit different sides of Rocambole's personality.
- Their mother was apparently Miss Ellen Palmure (Palmer?), who served as both Rocambole's opponent and love interest in The Miseries of London (1867-1868). Hélène is named after her paternal grandmother.
- Fatala was a Femme Fatale villain protagonist of another series created by Marcel Allain. She was active in 1930s. The theory goes that she was a daughter of Hélène, modeling herself after the exploits of her mother and maternal grandfather.
- Fantomette/Françoise Dupont was a Kid Hero, protagonist of a series of novels which started in 1961. 51 volumes had appeared by 2009, and more may eventually appear. The theory goes that she chose the codename to lay claim to the mantle of her ancestor Fantômas. But has more in common with Inspector Juve than most members of her line, while having similar skills to Hélène and Fatala.
- Satanas was a villain created by Gabriel Bernard, first appearing in 1922. His methods consisted of spreading fear and chaos, exactly like Fantômas. The theory is that Satanas was not merely a Captain Ersatz of Fantômas, but actually modelled himself after him. And that he was another family member laying claim to the mantle, possibly a grandson.
- Jean-Marc Lofficier has suggested Satanas as a good mate for Belphegor/Simone Desroches, the main villainess in the 1928 film of that name. A figure who dresses as a ghost to strike fear to the heart of her enemies.
- Diabolik first appeared in 1962, and also had the Master of Disguise abilities and ruthlessness of Fantômas. The theory is that the "orphan" actually is another scion of the same family.
- That would explain why his adopted father King was so surprised when he read the documents that revealed Diabolik's real name and made sure nobody knew it (not even Diabolik himself, who was always referred as 'Boy' until taking his more famous name). Still, the sheer coincidence of Fantômas' descendant ACCIDENTALLY modelling himself after him is frightening...