Salvatore "Sammy the Bull" Gravano is an American former mobster who rose to the position of underboss in the Gambino crime family of New York City before becoming a government witness. As the underboss, Gravano played a major role in prosecuting John Gotti, the crime family's boss, by agreeing to testify as a government witness against him and other mobsters in a deal. As part of the agreement, Gravano confessed to his involvement in at least 19 murders, although he was also responsible for a number of other crimes.