Complex sentence: Joseph "Mad Dog" Sullivan (born c.1940) was an Irish-American hitman who acted as a contract killer for the Mafia in New York City and was also rumored to be involved in the disappearance of Jimmy Hoffa.
Split into simpler sentences: Joseph "Mad Dog" Sullivan (born c.1940) was an Irish-American hitman who acted as a contract killer for the Mafia in New York City. He was also rumored to be involved in the disappearance of Jimmy Hoffa.