- "Today I settle all family business, so don't tell me you're innocent, Carlo. Admit what you did."
- ―Michael Corleone[src]
A half northern Italian, half Sicilian native of Nevada and former laborer, Carlo migrated to New York City following trouble with the law and became a friend of Sonny Corleone, through whom he met Sonny's sister Connie in 1941 at a surprise birthday party for Sonny's father Vito.
They were married on the last Saturday of August 1945 in a traditional Italian wedding at the Corleone mall, a compromise made in order to appease Vito, who was disappointed with his daughter's choice in a husband.
Rizzi and the Corleones
Carlo was thrilled at the prestige of being a member of the Corleone family, but Vito, disappointed his daughter had chosen an unworthy husband, instructed Tom Hagen not to allow Carlo significant knowledge of the family's workings, but to "give him a living". He was relegated to running a small sports book under the family's protection, reporting to top hitman Willie Cicci.
Frustrated at his minor role in the family business, Carlo regularly physically abused and cheated on Connie as a means of exerting his own power over the Corleones. The Don accepted Carlo's philandering and abuse, coldly refusing to intervene when Connie complained. In truth, Don Corleone was outraged at how Carlo treated Connie, but felt powerless to intervene since Italian tradition forbade a father from interfering in a daughter's marriage. However, Sonny, Fredo, Tom and Michael grew to hate Carlo for his mistreatment of their sister, though the Don instructed them not to interfere. Sonny, in particular, grew to despise Carlo so much that the two nearly came to blows, and Sonny had to be forcibly kept away from Carlo.
Sonny visited Connie one day after their father's near-assassination and discovered his sister covered in bruises after a particularly bad beating. She begged him not to do anything about it and he gave her his word. However, without the Don's calming influence, he lost his temper and beat Carlo mercilessly in the street in front of his book, threatening to kill him if he ever harmed Connie again. He actually let up on Carlo a little bit after realizing that Carlo refused to fight back; Sonny could never bring himself to kill a defenseless person. Soon afterward, Carlo was told that his book was being shut down as a result of the Five Families War. In a fit of pique, Carlo sought revenge by making a deal with the Corleones' rival Emilio Barzini to kill Sonny, which would break the stalemate of the Five Families War and possibly allow the other crime families to negotiate a deal to sell narcotics in Corleone territory.
- "That's it. Break it all, you spoiled guinea brat - break it all! C'mon now - kill me! Be a murderer like your father. Come on, all you Corleones are murderers anyway."
- ―Carlo Rizzi[src]
Carlo set the plan in motion by setting up a call from one of his girlfriends. Connie took the call and confronted him. Carlo curtly tells Connie, "Vaffanculo!" (Italian for "Fuck you!"), provoking Connie (who was pregnant with their child Victor) into an argument in which he beat her senseless. Connie called Sonny, who flew into a rage and set out to confront Carlo. En route, Sonny was killed by Barzini's men in a hail of gunfire at the toll booth on the Jones Beach Causeway. Fearful of being blamed by the Corleones, Carlo's treatment of Connie improved and he stopped beating her.
Vito forbade any investigations into his son's death, and concluded on his own that the Barzini family was responsible. In 1954, Michael became acting head of the family, and, with Connie's encouragement, began treating Carlo as a trusted lieutenant, sending him to help the family with union troubles and promising to make him his "right-hand man" once the family moved to Carlo's home state of Nevada. Carlo thought that he was getting the respect he deserved at last. In truth, Michael had discovered early on that Carlo had fingered Sonny, and was only keeping him close as a ploy to make him vulnerable. After Vito's death, Michael moved into the main house in the Corleone compound, and allowed Carlo and Connie to move into the smaller one he'd shared with Kay. He even stood as godfather to Carlo and Connie's second child Michael Francis at the behest of Kay, which took place at the same time as his massacre of the heads of the Five Families.
- "Michael! You lousy bastard -- you killed my husband! You waited until Papa died so nobody could stop you, and then you killed him. You blamed him for Sonny -- you always did. Everybody did. But you never thought about me - you never gave a damn about me."
- ―Connie Corleone[src]
Shortly after his son's baptism, Michael ordered Carlo to wait at his house. Carlo was waiting in his living room when Michael showed up with Tom, Al Neri and Rocco Lampone. To Carlo's surprise, Michael told him that he has known all along about his involvement in Sonny's death. Carlo denied any involvement, but Michael assured Carlo that, while he would be exiled from the family, his life would be spared. Carlo was calmed enough to confess his involvement with Barzini. When Carlo got into his car to leave, however, he was violently garroted by Peter Clemenza. Connie was enraged upon learning what Michael had done (though she likely didn't know of Carlo's involvement in Sonny's death), and resented him for some years afterward. However by 1959, after the death of their mother Carmela, Connie forgave Michael, realizing that he was trying to protect the family and do what he thought was necessary.
Carlo's murder was publicly pinned on the Barzini family.
Still his death had repercussions, because it marked the beginning of the end of Michael's marriage to Kay, who after this incident realized that her husband had become a true crime boss, willing to murder his own sister's husband and lie to her face about it.