Jack Lupino is a major captain of the Punchinello Crime Family in Max Payne. He was mentioned several times by Mafia thugs, especially by Vinnie Gognitti that Jack was going crazy, and indeed he was. (Vinnie even stated in a letter that he blew a thug's brains out because he wanted ot see what his brains looked like on the wall). Jack was freuently using Valkyr and was going insane, worshipping devils and believing he was a wolf and a messenger of Hell.
He is only seen in one chapter throughout the whole game and he was killed by Max shortly after. Max even shot him multiple times after he died, just to make sure he was 100% dead.
See Straight From A Bad Dream for more details.