Who ordered the hit on Fredo?
Death. Fredo, moments before his death at Lake Tahoe. Upon their mother's death, and at the urging of their sister Connie, Michael relented toward Fredo and seemingly offered reconciliation. However, it was only a deception to draw Fredo in so as to have him murdered by Al Neri.
No. Fredo believed that Michael had forgiven him at their mother's funeral. I imagine that he was afraid of angering his brother and abided by his decisions without question, as evident when Michael calls for Anthony before Fredo leaves. Besides, Fredo was too stupid to anticipate that his own brother would kill him.
While in Havana negotiating with Roth, Michael discovers that Fredo is the family traitor behind the assassination attempt on him.
While in Havana, Michael learned that Fredo betrayed him when Fredo accidentally let it slip that he and Johnny Ola had been to a sex show in Havana. He confronted Fredo at a New Year's party in Havana, telling Fredo that he knew he was the traitor, and that he broke Michael's heart.
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.
The kiss is known as "Il bacio della morte," meaning "the kiss of death." In this instance, it was to signify to Fredo that he was marked for death for betraying his brother to Hyman Roth (Lee Strasberg) and his right-hand man Johnny Ola (Dominic Chianese) in The Godfather Part II.
In film. 1974 The Godfather Part II produced, directed, and co-written (with Mario Puzo) by Francis Ford Coppola, Michael Corleone gives his brother Fredo Corleone the kiss of death after he discovers Fredo's betrayal.
In the movie "The Godfather," Vito Corleone realized that Tessio was the traitor when he asked to set up a meeting between Michael and Barzini, who was one of the rival gang leaders. Vito knew that this meeting would be a trap and that Tessio had betrayed the family by working with Barzini.
Betrayal. Tessio seals his fate by relaying Barzini's deal to Michael. Tessio thought more of Vito's younger son Michael than Clemenza or Tom Hagen did, but never believed he was powerful enough to keep the family going after he was named his father's heir.
Yes. In Godfather 3 while in Sicily Michael tells Kay of all the hours he spent in his room at Don Tommasino's estate thinking of her. Kay replies, “But then you got married.”
Did Pentangeli betray Michael?
In The Godfather Part II, Frank Pentangeli is portrayed as having been one of godfather Vito Corleone's (Marlon Brando) most trusted associates. A rift grows between Pentangeli and Michael, however, that eventually results in Pentangeli betraying the family.
It's one of the most memorable scenes in movie history: Al Pacino, as Michael Corleone grabs his brother Fredo's (the late, great John Cazale) face, gives him a long kiss on the lips and says, "I know it was you, Fredo. You broke my heart.

Michael asks if Roth would object to him having Frankie killed. 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.
Fredo betrayed Michael by working with Johnny Ola and Hyman Roth behind the scenes, when the Corleone and Roth organizations were negotiating a business deal.
When Michael Corleone fled to Sicily to escape the American authorities, Calò and his friend Fabrizio were assigned to protect Michael. The three developed a close bond of friendship until Fabrizio betrayed Michael, attempting to kill him in an explosion that claimed the life of Michael's wife Apollonia.
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.
2. Casino mogul Moe Greene's life and death mimics real-life mobster Bugsy Siegel's. In The Godfather, Moe Greene is credited with putting Las Vegas on the map. In reality, it was Jewish mobster Benjamin "Bugsy" Siegel, who built the Flamingo, now the oldest resort on the Las Vegas Strip.
Fictional biography and early years. Vito Corleone is based on a composite of mid-20th century New York Mafia figures Carlo Gambino, Frank Costello, Joe Bonanno, and Joe Profaci. The character's story begins as Vito Andolini in Corleone, Sicily, in the Kingdom of Italy.
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.
Of course, it is at this moment that Michael realizes it was Fredo who betrayed him to Hyman Roth, as in the previous scene Fredo pretended to have just met Johnny.