The most famous Chicago gangster was Al Capone, who was active in the 1920s and 1930s. He was a notorious mob boss and leader of the Chicago Outfit, a powerful organized crime syndicate. He was known for his illegal activities such as bootlegging, gambling, and prostitution. He was also known for his violent tactics and his ability to evade law enforcement. He was eventually convicted of tax evasion and served time in prison.