Frank 'The Enforcer' Nitti has been portrayed by Hollywood as a vicious gang land thug, Capone trigger man and smooth talking cocky gangster. In Brian DePalmers 1987 movie "The Untouchables", the cinema going and video watching public were introduced to Nitti as the nemesis of Elliot Ness and his band of federal agents. The movie even goes as far to show Nitti dying at the hands of Ness, falling from the roof of the Chicago court house where Capone was being tried.
This is all complete nonsense.
Frank Nitti began his criminal career as a barber with a rather shady clientele. His customers would come to him to fence various items of stolen merchandise. It was while in this role that he came to the attention of John Torrio and Al Capone since he had a proven network of underworld characters able to peddle illegal booze. Nitti became a whiz at smuggling Canadian whiskey into Chicago and to the various distribution points throughout the City. By the mid twenties, he was a high ranking member of the Capone Mob.
With the conviction of Al Capone in 1929, Nitti became the boss of the Chicago Mob. At least that is what the press and law enforcement agencies were believing. So high profile was the coverage of the Mob in those days, that Nitti was a natural choice for the press. Nitti probably believed it himself. In fact, it was Paul 'The Waiter' Ricca who carried the flame of the Mob after Capone. Ricca was quite happy to let Nitti think he had control, but there were often times when Ricca would countermand a Nitti decision with a quick "We'll do it this way and let's say no more about it". Nitti was never made a member of the Commission (a board of directors of all the Mafioso families) but Ricca was, secretly, without Nitti's knowledge. It was only the presses spotlight on Nitti that made him important. This would draw attention away from the real workings of the Chicago Outfit.