Salvatore "Sammy the Bull" Gravano (born March 12, 1945) was a high ranking member of the Gambino crime family. A capo and then later Underboss to John Gotti, he is probably most known as the man who brought Gotti down by becoming an FBI informant.
Originally a soldier for the Brooklyn faction of the Gambinos, he was part of a conspiracy within the family to murder Gambino boss Paul Castellano. Gravano played a key role in planning and executing Castellano's murder; other conspirators included John Gotti, Angelo Ruggiero, Frank DeCicco, and Joseph Armone. The conspiracy would elevate Gravano's position in the family to Underboss under Gotti. Gravano is also known as "King Rat" because of his testimony against Gotti. His testimony drew a wave of Cosa Nostra members to become informants.