Frank Sheeran was a World War II veteran who first found his way into organised crime after he was discharged from the army in 1945. Though by day he worked as a truck driver, by night he made extra money as a hitman. Eventually he grew to be a close associate of Mafia boss Russell Bufalino, head of the Bufalino crime family, who acted as a mentor for Sheeran.
With Bufalino's help, Sheeran began working with Jimmy Hoffa, an infamous labor union leader who then served as the president of the International Brotherhood of Teamsters, a union that historically suffered from corruption and control by organised crime. Sheeran earned Hoffa's trust and eventually became a top Teamsters Union official, while still acting as the Bufalino crime family hitman and top aide to Bufalino himself.