Al Capone is the leader of the Chicago mafia and one of the main antagonists in Tintin in America.
Capone sent his mobster underlings to kidnap Tintin for writing up a report on the Chicago mafia organizations. Tintin was brought to Al Capone who tries to stop him. Tintin escaped from his captors and tried to tell his story to the police. The police rejected his pleas so Tintin meets Capone's rival Smiles but he was unwilling to join his gang so he left Smiles. In the animated version of the story, all of Chicago's mafia organization work for Capone.