6. Jimmy Hoffa
From 1958 until 1971, Jimmy Hoffa was in charge of the International Brotherhood of Teamsters (IBT) union. While the union saw tremendous growth during that time, Hoffa was involved in some shady stuff, including ties with the mafia and convictions for several crimes.
In July 1975, Hoffa told his family and some close friends that he was seeing mobsters Anthony Provenzano and Anthony Giacalone. Later that night, he called his wife, saying that the men were late but he would keep waiting for them.
That was the night when Hoffa disappeared. Over the years, several people have been accused of killing Hoffa, and some have even confessed, but there has never been any evidence to back up the claims.