Salvatore Tessio

Tessio befriends Peter Clemenza and Vito Corleone and they begin their criminal careers as low-level hoodlums in the New York City neighborhood of Little Italy in Manhattan; As Vito rises to power and prominence in the Mafia underworld, Tessio and Clemenza become his trusted caporegimes. Eventually Vito splits Tessio from Clemenza and asks the two not to socialize unless absolutely necessary, both to remove the threat of a conspiracy against him and also to set up Tessio to function as a "safety valve caporegime" whose Mafia soldiers can be called upon by the Corleone family in emergencies. Tessio establishes his regime in Brooklyn, where he is well-connected, and owns the Embassy Club as a base of operations.

Most federal investigators consider Tessio the smarter, savvier, and more ruthless of the Corleone capos. However, according to the book, he mellows considerably over the decade of peace between New York's Mafia families. One of the strengths of the Corleone Family is that, given Tessio's control over Brooklyn, some enemies do not know that Tessio's regime functions within the Corleone Empire, and thus do not understand the extra strength it has.

When Vito is shot and wounded by drug lord Virgil Sollozzo's men, igniting a war among the Five Families, Tessio serves as the right-hand man of Vito's eldest son Sonny, who runs the family while Vito is incapacitated. In the novel, Tessio is depicted as thinking more highly of Vito's youngest son and eventual successor Michael than do Clemenza and Corleone family consigliere Tom Hagen. However, he never completely trusts Michael, and is frustrated when Michael prevents him from retaliating against rival Don Emilio Barzini as the Barzini family chips away at his bailiwick in Brooklyn. Ultimately, Tessio betrays Michael by helping arrange his assassination at a peace summit with Barzini and Philip Tattaglia. The summit will be held in Tessio's fiefdom in Brooklyn, where Michael will presumably be safe. In return, Tessio was to inherit the Corleone family upon Michael's death.

In the novel, Tessio helps broker the summit shortly after Vito's death. In the film, Tessio approaches Michael at Vito's funeral about setting up the peace summit, Michael already anticipated the plot via his father's warning: whoever approached Michael about the peace summit would be the family traitor. Tessio's betrayal surprises Hagen, who thought Clemenza would be the one to betray Michael. Michael tells him, "It's the smart move; Tessio was always smarter."

A few days later, Tessio is ready to escort Michael and Hagen to Brooklyn for the meeting when Willi Cicci informs Tessio that Michael is going separately. A frustrated Tessio says it interferes with his "arrangements". Hagen says he cannot go either, and several hitmen surround Tessio. Immediately understanding his situation, Tessio calmly tells Hagen to tell Michael that his betrayal was not personal, but simply business. Tessio asks Hagen to get him off the hook, but Hagen declines. Accepting his fate, Tessio goes quietly as he is taken away to be killed.

Mario Puzo's original novel and the film imply Tessio's death, but Mark Winegardner's sequel novel The Godfather Returns explains that he is executed with a gunshot at point blank range by his enforcer Nick Geraci. In this novel, Geraci is chosen and intended to succeed him as capo, but in the original novel, Al Neri takes over the old Tessio regime.

In the video game adaptation, Tessio is the main hit contractor for the first half of the game's story. Later, after he is confronted by Tom Hagen and Cicci, Tessio is escorted to the place where he was to betray Michael by the game's protagonist, Aldo Trapani. He subsequently flees, but is hunted down and shot by Trapani. In the game, Tessio's death takes place before the baptism executions, unlike in the film.