Complex sentence: Lucchese was a founding member of the American Mafia (Cosa Nostra) and was the boss of the Lucchese crime family which is one of the Five Families in New York City from 1951 until 1967, when he died from a brain tumor.
Split into simpler sentences: Lucchese was a mobster and founding member of the American Mafia (Cosa Nostra). He was the boss of the Lucchese crime family, one of the Five Families in New York City from 1951 until 1967, when he died from a brain tumor.