Jimmy Darmody (Michael Pitt) is Nucky’s protege, a Princeton dropout and WWI vet with brains and a vicious bite. His character is loosely based on Jimmy Boyd, who was Nucky’s assistant when he was head of the 4th Ward and county clerk. The show has Jimmy robbing bootleggers, which he did not do. He also was not involved in any way with Al Capone, but he was responsible for delivering bad news and helping maintain order in his ward.
Agent Nelson Van Alden (Michael Shannon) is the overzealous FBI agent trying to purify Atlantic City and rid the country of liquor by any means necessary (even if it means taking the law into his own hands). His character is based on William Frank, who oversaw a joint IRS and FBI task force to bring Nucky to justice. The only problem is that his operation began in 1936, which is well after the show’s setting. Either way, seeing Shannon on the small screen in Boardwalk Empire will tide us over until he plays General Zod in Man of Steel.
Margaret Schroeder (Kelly MacDonald) starts off as one of Nucky’s loyal followers, but after she is beaten by her abusive alcoholic husband (who ends up dead via Nucky’s brother), she becomes his mistress. Her character is loosely based on Mary Ill, who was also involved with local women’s groups and charities. Her extensive interviews were used as research for the book and helped to create Nucky’s character in the show. However there is no evidence that she and Nucky became romantically involved, or that he arranged for the brutal murder of her husband, although at least one source claims he did have the man banned from local gambling halls, as is depicted in the show.