Frank received Academy Award, Golden Globe and BAFTA Award nominations for his performance as William Shakespeare’s Iago in Stuart Burge’s 1965 film of Laurence Olivier’s staging of Othello. He also won the Best Actor Award at the San Sebastian International Film Festival.

He later essayed the definitive screen portrayal of Alexandre Dumas’ musketeer Porthos in three movies for director Richard Lester: The Three Musketeers (1974), The Four Musketeers (1975) and The Return of the Musketeers (1989). Frank’s many other films include The Longest Day; Tony Richardson’s The Lonliness of the Long Distance Runner; Martin Ritt’s The Molly Maguires; Bob Clark’s Murder by Decree; Alan Bridges’ The Return of the Soldier (for which he recieved a BAFTA Award nomination); Franco Zeffrelli’s Sparrow; and Eric Styles’ Dreaming of Joseph Lees; and most recently Roman Polanski’s multi-award winning The Pianist and Norma Jewison’s The Statement.