Al Capone was an infamous gangster during the Prohibition era.
Capone in the Timeless Universe
In the original timeline, after a long history of criminal activity, Al Capone was finally arrested over tax evasion on March 13, 1931.
In the altered timeline, Garcia Flynn prevents Capone from being charged with tax evasion. This means that Capone owes Flynn. Flynn also tells Capone the location of Prohibition agent Eliot Ness. Capone has Ness killed by one of his gangsters. To repay Flynn, Capone arranges a meeting with Flynn and the Chicago Mayor William Hale Thompson. Flynn interrogates and kills Mayor Thompson, gaining the information that Rittenhouse has meetings every twenty-five years in Washington D.C.
Later, Richard Hart, Al Capone's estranged older brother, arrives at Capone's residence with Lucy Preston, Wyatt Logan, and Rufus Carlin. Capone is ecstatic to meet Hart again after so many years, but this joy quickly fades after Hart tells Capone that he's here to arrest him. Guns are drawn. Capone points a gun at Rufus, claiming that killing Rufus is the other favor he owes Flynn. Hart points a gun at Capone, and so does Wyatt. Frank Galluccio, one of Capone's top men, points a gun at both Lucy and Rufus. Capone shoots Rufus, but is then fatally shot by Hart. In the altered timeline, Capone dies on March 13, 1931.
Al Capone at Wikipedia