If you want to learn more about Joe Colombo as boss, check out Scarpa's FBI files and also "Body Mike" by Joey Cantelupo.

He sounded like a decent guy as far as mob bosses go. Then he went nuts with the League. To say he was Gambino's puppet might be too much, but he owed his position as boss and earned a lot of money because of Gambino so would have been loyal to him.