Walter John Buchanan (2 April 1890 – 20 October 1957) was a British theatre and film actor, singer, dancer, producer and director.

Born to a comfortable middle-class family in Scotland, Buchanan attempted to follow his father into auctioneering, but conceived a strong desire to be a performer. After a calamitous début as a stand-up comic, he moved to London and between 1912 and 1917 built up a performing career in the chorus or small parts in musical comedies before achieving leading roles in West End shows and remaining at the top of his profession for the rest of his career.

He was known for more than three decades as the embodiment of the debonair man-about-town in the tradition of George Grossmith Jr., and was described by The Times as the last of the knuts. Among his leading ladies in West End, and, later, Broadway, shows were Binnie Hale, Gertrude Lawrence, Beatrice Lillie, Jessie Matthews, Phyllis Monkman and – the partner with whom he was most associated – Elsie Randolph.

Buchanan directed, choreographed, and produced many shows, and ran theatres and a film studio. He made several British films, often adaptations of his stage successes, but his best-known film was the Hollywood musical The Band Wagon in 1953.