Actor. He is most identified with the role of Detective Danny “Danno” Williams in the long-running police drama “Hawaii Five-O” (1968 to 1979). The line “Book ’em, Danno”, often used during the series’ run, is one of the most memorable in television history. He was adopted as an infant by playwright Charles MacArthur and legendary stage and film actress Helen Hayes; there was little doubt he would follow them with a career in the entertainment industry. An exceptional athlete during his high school years, he excelled at football, baseball and basketball, while participating in the Drama Club. He made his TV debut in a 1955 episode of the program “Climax!” titled “Deal a Blow”, and appeared in his first motion picture role two years later in “The Young Stranger”. He would receive a Theatre World Award in 1961 for his performance in the Broadway play “Invitation to a March” (1960 to 1961). During the 1960s, MacArthur had scores of TV guest roles on such programs as “Wagon Train”, “Bonanza” and “Gunsmoke”, while having substantial parts in the films “Kidnapped” (1960), “Swiss Family Robinson” (1960), “Spencer’s Mountain” (1963), “The Bedford Incident” (1965, as the panicked Ensign Ralston), “Battle of the Bulge” (1966), “The Angry Breed” (1968) and “Hang ‘Em High” (1968). He was formerly married to actress Joyce Bulifant.