Donal "Donald" O'Brien (15 September 1930 – 29 November 2003) was an Irish film and television actor. In his near 40-year career, O'Brien appeared in dozens of stage performances and in more than 60 film and television productions.

O'Brien made his feature film debut in 1953 with Anatole Litvak's war drama Act of Love. He studied acting in Dublin and initially joined the Gate Theatre at age 19 before making the transition to film several years later. O'Brien's performance in The Train (1964), in which he played a Wehrmacht Feldwebel, led to his first break-out role in Grand Prix (1966) starring alongside James Garner and Eva Marie Saint.

He was particularly known for his performances in the Spaghetti Western genre of the late-1960s and '70s, with memorable roles in Run, Man, Run (1968), Four of the Apocalypse (1975), Keoma (1976), Mannaja (1977) and Silver Saddle (1978), as well as later appearances in Italian horror, post-apocalyptic, and zombie films. In 1980, O'Brien suffered a head injury which left him in a coma for three days and partially paralysed. Though eventually recovering from his injuries, his mobility was significantly limited for the rest of his life. In spite of this, O'Brien continued to work for another decade in the Italian film industry, almost exclusively for directors Lucio Fulci and Joe D'Amato. His last years included supporting roles in The Name of the Rose (1986) and The Devil's Daughter (1991).