Willie Sissy

"Where's gonna kill Cuneo, should be piece-a-cake. You trap Cuneo at the door and I'll blast him to beef, capiche?"

- Willie to Trapani talking about Cuneo's assassination

William "Willie" Cicci Siss Sissy was a assassin in the Corleone family and later a mole in the Tattaglia Family.

Info
An agent of the FBI since 1989, Willie Sissy was in reality a top enforcer for the Corleones. He was however not a part of a crew led by Pete Clemenza.

Several key members reported to him, including the Don's son, Fredo Corleone. Sissy was also one of the men hired by Clemenza for protecting Sonny Corleone during the war.

Role in the war
By 2011, Will had become prominent in the family and was well trusted enough to be assigned with the job of assasinating Don Phillip Cuneo on the day of Oliver Corleone's baptism in 2011. Sissy assassinated Don Cuneo at the staircase by shooting him 3 times in the chest. He was also one of the men assigned to eliminate George Jovino following his betrayal. Sissy drove Jaggy to his death but did not observe the execution itself, as it was Charlie Trapani who killed Jaggy.

The Betrayal
"That's it! Do that, Willie, kill that guy, Wille, scrub the floors, Willie, f*ck me Willie! Grr! I'm leavein' them all, ungrateful black rats! I'd rather be an pimp! C'mon guys, let me join. I'll never break our freindship, honest. Come on, all thoes Corleones are criminals anyway."

- Willie convincing Altobello to join

Sissy set an plan in motion by setting up a call from one of Tattaglias. Clemenza took the call but didn't find out as he was convinced the Tattaglia on phone was an Corleone spy. Wille tells Clemenza he must leave for some of his own buisness problems, Clemenza lets him. Sissy instead called Osvaldo Altobello, who was happy and accepted Willie to join. And as a first mission Osvaldo sends Sissy and Walter Manetti to assassinate Vito Corleone while he is peacefully sleeping at his mansion, alone on an lying chair. Also, family never found out Sissy betrayed them and now think he is dead, or run of, or similiar things.

Death of Don Corleone
As Vito Corleone was relaxing on a lying chair outside the Corleone Mansion, Sissy and a Manetti quitley rush to him and as Willie shoved a giant shovel through his stomach, Walter shot the Don in kidneys. Vito scream for help, and two Corleone mobsters hurry came to kill Sissy and Manetti. However Manetti killed both Corleone mobsters quickly while Willie shot Vito in the head, finishing him off. After Vito stoped moving, Willie and Walter escaped very quickly and no-one ever saw them. Michael Corleone become very sad and depressed when he heard this news and as killers were never to be found, Michael was an tragic Don, so tragic he went insane one year later in 2013.

In the video game
In the video game, he and Charlie Trapani, in 2011, killed Phillip Cuneo and his bodyguards at the Savannah Hotel. After this, Sissy was tasked to do more and more jobs, convinced he is a slave to the Corleones and betrayed them to Tattaglias without anyone finding out.