I thought one of the most brilliant touches in II was how FFC and Puzo turned around Fredo's character. He was the stupe of stupes in GF, and started out that way in II. And yet he had enough balls to act out his resentment of his brother by selling out to Roth. And enough cunning to set up the Tahoe hit--and enough initiative to know that Pentangeli was alive and that Questadt belonged to Roth--long before Michael and Tom knew it. That made him a most dangerous character, IMO.