Lupino is mentioned several times by Mafia thugs, especially by Vinnie Gognitti. Gognitti writes that Jack was going crazy, and that he even blew one of his thug's brains out only because he wanted to see what they would look like on the wall. Lupino is addicted to valkyr and is clearly insane, worshipping devils and believing that he is a wolf and a messenger of Hell.
Behind the scenes
Jack Lupino and his nightclub Ragna Rock contain many allusions to Norse mythology. "Lupino" is a surname of Italian origin, meaning "little wolf". Jack Lupino continually makes references to wolves and calls himself "the Fenris Wolf." The Fenris Wolf (also known as Fenrir) was a monstrous wolf and son of Loki who was supposed bring about and play a huge role in Ragnarök - the Norse apocalypse.
Jack is surrounded by cultists wielding shotguns, Molotov cocktails, and Ingrams. Keep moving and keep firing with a cool head. Despite his somewhat intimidating demeanor, Jack himself is probably the easiest boss in the game; he uses a sawed-off shotgun and, after he fires his first two shots, he is completely open to any sort of attack. It is possible to even bludgeon him to death easily with a baseball bat. Every time he is hit while he is reloading, he is forced to start his reloading animation over again. To sum it up, kill his henchmen, dodge his first two shots, then finish him off with the weapon of choice.
Max loses all his weapons after his fight with Lupino. Therefore, ammo conservation should not be required when fighting him.