The person who most directly betrayed him was his bodyguard Fabrizio, who planted the bomb in his car that killed his wife
Hyman Roth agrees to the hit. This was done by Michael to give Roth a sense of security and superiority that Michael was wrong about who ordered the hit. Michael then goes to Frankie to reveal that he knows it was actually Roth behind the hit.
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.
Roth secretly plans to assassinate Michael, partly to avenge Moe Greene's murder (as depicted in The Godfather). Roth instructs Ola to befriend Michael's brother Fredo, who provides Ola (and Roth) information about Michael that enables them to make an attempt on his life.
Paulie has seemingly betrayed Vito—and thus the family—by selling him out. In The Godfather, this kind of betrayal is the worst of all sins. We see the matter discussed, in the Corleone family office, just before the viewer spends time in front of Clemenza's cozy abode.
How did Vito Corleone know whomever approached Michael Corleone to set up a meeting with the Emilio Barzini would be the traitor? Because as much as Vito had earned the loyalty of Peter Clemenza and Sal Tessio, he also knew that every capo has a limit; and loyalty never automatically transfers from father to son.
David Chase instead offered him the role of playing Paulie Gualtieri, Sirico agreed under the condition that his character would not "become a rat". Paulie begins the series as a soldier, later becoming a caporegime in the DiMeo crime family. He is violent, impulsive, and paranoid.
After telling Michael that he has never met Ola, Fredo later carelessly tells Geary that he had been to a nightclub with Ola. Michael overhears the conversation and realizes that Fredo betrayed him to Roth.
A rift grows between Pentangeli and Michael, however, that eventually results in Pentangeli betraying the family.
Fredo betrayed his brother to rival gangster Hyman Roth, who used him as a pawn in a plot to destroy the Corleone Family. Fredo provided unspecified information on the Corleone family in return for receiving compensation (what kind is never specified) independently of the family.
Michael Corleone met with Rocco Lampone and arranged for him to kill Hyman Roth at the Miami Airport. Simultaneously, Al Neri was tasked with the killing of Fredo for his betrayal.
When Sonny found out, he ordered Clemenza to have Paulie – "that stronz" (Italian for «turd»), as Sonny called him–killed on the spot. Clemenza considered Paulie's treachery to be a personal affront, and was only too happy to arrange Paulie's execution.
At the very end of the movie, Michael lies to his wife, Kay, about having Carlo killed. This shows that he's set his course: she won't be able to be a part of his real world and will be shut out from seeing his true, ruthless nature in action.
Enraged, Sonny speeds towards Connie's apartment in Hell's Kitchen ahead of his bodyguards. At the Long Beach Causeway toll plaza, Barzini's men trap Sonny and shoot him to death. During a meeting with the other crime family dons to establish peace, Vito realizes that Barzini masterminded Sonny's murder.
We know Fredo betrayed Michael by working with Hyman Roth and Johnny Ola. What exactly did he do though? He says he didn't know it was going to be a hit and that he was only trying to help the family.
Woodcut of Al Pacino. When Francis Ford Coppola and Paramount Pictures set out to cast the role of Michael Corleone in The Godfather, they had a disagreement. The studio wanted Robert Redford, Warren Beatty or Ryan O'Neal.
While Tom Hagen initially suspected Clemenza of being the one who would betray Michael to Don Emilio Barzini's alliance, Michael reasoned that the more cunning Tessio was the culprit. Clemenza's strongest attribute to the Corleones was his stubborn loyalty, not his intelligence.
Fabrizio was a bodyguard to Michael Corleone who was hiding in Sicily. Fabrizio betrays Michael by setting up explosives in his car, but kills his new bride instead. In the novel, Fabrizio is later shot dead in revenge for the killing.
He then flees to Sicily, where he falls in love with Simonetta Stefanelli's Apollonia. Tragically, she's later killed in a car bomb planted by Michael's bodyguard Fabrizio (Angelo Infanti), who betrayed him to his enemies. While Michael gets revenge on those who ordered the hit, Fabrizio is never seen again.
2. Michael and Vito might have placed some of the blame for Sonny's assassination on Tom. Though it turns out that Carlo Rizzi plotted with Barzini to set Sonny up, Michael and Vito probably believed that Tom didn't do enough to stop Sonny from leaving the safety of the family compound that day to find Carlo.
Meanwhile, Kay decides to leave Michael and take their children with her, believing Michael will always live in a world of crime and violence. Michael asks her to reconsider, but Kay reveals she aborted their unborn son because she refused to bring another of his children into the world.
Because Fredo remained a threat to his family. As long as Fredo was bitter about being stepped over, and he always would be, he was a threat. Michael triumphed over his enemies because he was cold, ruthless and logical.
However, despite his seniority, Paulie is one of the more eccentric of Tony's associates and is arguably one of the most ruthless, as expressed by his paranoia, mysophobia, competitiveness, miserly nature, impulsive violence and often childlike dependence on Tony's approval.
Paulie cut a deal with New York where he would arrange the assassination of Tony and declare himself the new boss of the DiMeo family. New York would back it with their muscle and influence to make sure Paulie's coup is seen as legitimate within the remaining Soprano family and the Five Families.
Offsetting Tony's suspicions is the swiftness in which Jimmy went out on bail for his offense - only four hours after arrest. Plus, the fact that Jimmy also knew about a new forensic technique that lifts fingerprints from money and has generally suspicious body language substantiates Tony's accusations against him.