Final answer:
Al Capone, the notorious '20s mobster, was responsible for beating up the mayor of Cicero on the steps of city hall, benefiting from corrupt local police to maintain his criminal empire.
Step-by-step explanation:
The '20s mobster who beat up the mayor of Cicero, Illinois, on the steps of city hall as a nearby cop looked away was Al Capone. Capone, also known as "Scarface," was one of the most infamous gangsters in Chicago during the Prohibition era. His criminal operation, known as the Chicago Outfit or Chicago mafia, was involved in a variety of criminal activities, including bootlegging, prostitution, gambling, and murder. Capone's operation was able to flourish in part because he had local police on his payroll and was thus able to act with relative impunity. While Lucky Luciano was another leading gangster of the time, it was Al Capone who became infamous for his role in terrorizing Chicago and controlling its illicit liquor trade.