FREDO CORLEONE IN THE GODFATHER PART II (1974)
His younger brother, the Godfather, Michael Corleone (Al Pacino). Sick at being passed over for the top spot in favor of his more competent sibling, Fredo (John Cazale) decides he wants his own piece of the mafia pie. To get it, he provides vital information about his brother to business-associate-turned-enemy Hyman Roth (Lee Strasberg), who uses it in an assassination attempt on Michael's life. Needless to say, this just breaks Michael’s poor little heart.
Punishment for snitching:
Michael disowns his brother but agrees to spare his life. That is, until their mother dies, at which point he has his bodyguard turn Fredo's brains into chum while they're out fishing.