Guido Martelli was once a henchman of Angelo Bronte. After Bronte's death in 1899, and at some point before 1907, Guido Martelli became the new crimelord of Saint Denis. He also bribed Benjamin Lambert, the police chief, to ignore the Italian mob's criminal activities.
Guido Martelli is mentioned briefly by Charles Smith as being the leader of the city's organized crime, with whom he made a deal to throw a boxing match. However, Charles bet on himself and does not throw match - he defeats his opponent and, as a result, wins a lot of money for betting on himself to win. Frustrated at being tricked, Martelli's men track down Charles in order to get revenge and their money back. Four of Martelli's men confront Charles and John Marston on the dockside, but are swiftly gunned down by the pair. Charles and John make their escape, where Charles says it's imperative that they do not get caught by the police, as there would be no chance of denying any wrongdoing, and that Martelli would ensure that they "wouldn’t get out of the interview room", reflecting his high level of control over the Saint Denis Police Department. After this, Guido Martelli is not mentioned again.
- Red Dead Redemption 2
- "Bare Knuckle Friendships" (mentioned)
- Despite not appearing in the game, Guido Martelli is credited with having a voice actor - Emanuele Ancorini.
- The player can encounter his men in a random encounter at Doyle's Tavern.