I was going to say he wasn't necessarily a boss, but LaPietra was ruthless. Between Ricca, Accardo, Giancana, and Aiuppa, I'd say you could make a case for all of them. They were dropping bodies everywhere. Chicago was always known for being pretty vicious and not taking chances. Aiuppa stands out to me though because for one, I think he is one of the spookiest looking dudes I've ever seen. Seeing photos of him is like looking at death. And for 2, during his reign as boss in Chicago during the 70's and 80's people were getting whacked left and right. Have to assume he ordered or gave the ok on the vast majority of those.