He is played by Academy Award-nominee Richard Castellano[1][2] in Francis Ford Coppola's 1972 film adaptation of the novel, and by Bruno Kirby (as a young man) in The Godfather Part II (1974).

Born near Trapani, Sicily, Peter Clemenza is one of Don Vito Corleone's caporegimes and oldest friends, as well as the godfather of his eldest son, Sonny.

He has a reputation as a superb judge of talent; his regime produced five future capos—Sonny, Frank Pentangeli, Rocco Lampone, Al Neri, and Joey Zasa.

For example, he is ordered by Don Corleone, via consigliere Tom Hagen, to oversee the punishment of two teenage boys who received suspended sentences for beating and attempting to sexually assault the daughter of undertaker Amerigo Bonasera.

When Gatto is implicated in drug kingpin Virgil "The Turk" Sollozzo's assassination attempt on Don Corleone, Sonny – now Vito's heir apparent – orders Clemenza to execute him.

Clemenza has Gatto drive him and Lampone around for several hours on the pretext of locating housing ("mattresses") for Corleone soldiers in the event war breaks out with the other Mafia families.

One of their lines of business is selling stolen dresses door-to-door; a deleted scene depicts Clemenza charming his way into the apartment of a young housewife and emerging a little later, having presumably had sex with her.

Clemenza's gradual takeover of the Corleone empire (with Vito and the other capos dead, he assumes a more prominent leadership role) in New York is briefly covered in The Godfather Returns, Mark Winegardner's 2004 sequel to Puzo's original novel.

Most noteworthy, the novel depicts Clemenza's fatal heart attack (mentioned in The Godfather Part II), and the many conspiracy theories that he had actually been murdered by the Rosato Brothers, former Corleone soldiers who had formed their own gang after a dispute over the future of the family.