Karl Swenson (July 23, 1908 – October 8, 1978) was an American theatre, radio, film, and television actor. Swenson is remembered for his role as the doomsayer in the diner in Alfred Hitchcock's The Birds (1963) and as the voice of Merlin in Disney's The Sword in the Stone (1963). On television, he had numerous credits in guest roles on various shows, especially Westerns, including episodes of Bonanza, The Virginian, and Gunsmoke. He had a major recurring role as Walnut Grove founder Lars Hanson on Little House on the Prairie (1974 - 1978).

Swenson also had roles in The Prize (1963), Major Dundee (1965), The Sons of Katie Elder (1965), The Cincinnati Kid (1965), Seconds (1966), Hour of the Gun (1967), ...tick...tick...tick... (1970), The Wild Country (1970), Vanishing Point (1971) and Ulzana's Raid (1972).

Born in Brooklyn, New York of Swedish parentage, he originally planned to be a doctor and studied at Marietta College before pursuing acting. Swenson appeared extensively on the radio from the 1930s through the 1950s. He entered the film industry in 1943 with two wartime documentary shorts, December 7 and The Sikorsky Helicopter. Swenson was married to actress Joan Tompkins. He died of a heart attack at Charlotte Hungerford Hospital in Torrington, Connecticut on October 8, 1978, shortly after filming the Little House on the Prairie episode in which his character dies. The episode aired on October 16, 1978, eight days after Swenson's death. He was interred at Center Cemetery in New Milford, Connecticut.