Mine would have to be hands down Tony Accardo. It's been said that Tony Accardo had more brains before breakfast than Al Capone had all day. They didn't call him Joe Batters for no reason. He was a soldier/muscle for Capone and its been said that even Capone thought he was a scary individual. Capone gave him his nickname Joe Batters and he also apparently saved Capone's life on a couple occasions. He went on to become what I would say the biggest, longest running, and most powerful boss in Chicago's history of Organized Crime. I'm pretty sure even though Giancana, then Aiuppa were labeled Boss he was always the Boss. Just used Giancana to be the face of The Outfit because Giancana loved the limelight. Aiuppa was also a very smart and good Boss. Together him and Accardo pretty much ran Las Vegas from Chicago. Of course along with other Outfit leaders from Kansas City, Milwaukee and Detroit. In my opinion he was probably one of the most powerful Bosses in the history of Organized Crime. Hands down my favorite!