Jimmy Saviano was a member of the Falcone crime family.
He technically had seniority over Fish Mooney, so when her scheme to use Nikolai to off the old man fell through, she turned to Jimmy for support in a coup. Since Jimmy had ambitions to sit in the big chair himself, he was less than receptive. In fact, he turned to his old buddy Butch and tried to enlist him in removing Fish from the picture. Having weighed his options, Butch decided he was better off with Fish, and killed Jimmy himself, after an apology for an incident in teenage when he stiffed his friend of his share of a robbery.