Sir Alec Guinness in the 1957 film Bridge On the River Kwai. Guiness played Lt. Colonel Nicholson, the overly-rigid officer of a British prisoner of war unit in Japan in World War II.
Alec Guinness won the Academy Award as best actor for the role. The film won six other Oscars, including best picture and best director for David Lean.
(And yes, 20 years later, Guinness played Obi-Wan Kenobi in the film Star Wars.)