Originally a mobster for the Colombo crime family, and later for the Brooklyn faction of the Gambinos, Gravano participated in the conspiracy 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. After Castellano's death, Gotti elevated Gravano to consigliere, a position he held until he became underboss in 1989. In 1991, he became a government witness. At the time, Gravano was the highest-ranking member of The Italian-American Mafia to ever break his Cosa Nostra oath and cooperate with the government. His testimony drew a wave of Cosa Nostra members to also become government witnesses.