Before the advent of computers and CGI movies used a variety of approaches to achieve animated special effects. One approach was stop-motion animation, used famously in King Kong (1933). The work of Willis O'Brien in Kong inspired Harryhausen to work in this field.
From his first demo reel, of fighting dinosaurs from an abortive project called Evolution, Harryhausen found work with Paramount, working on George Pal's Puppetoon shorts. During the war he worked for the Army Motion Picture Unit, from this work he acquired several million feet of unused film on which he made a series of fairy tale based shorts. This work led him to his first major film, Mighty Joe Young (1949) and then The Beast From 20,000 Fathoms (1953). It was on the Warner stage that he first used split-screen projection, allowing his miniature figures to apparently interact with real actors.
Harryhausen then moved to Columbia and began a fruitful partnership with Charles H. Schneer. Their first release was It Came From Beneath The Sea (1956), but the first proper result was The Seventh Voyage of Sinbad (1958) which Harryhausen also wrote. Always working alone on his effects it often took a long time for his movies to be made, after The Beast From Space (1957) and The Three Worlds of Gulliver (1960) his next success was with his masterwork - Jason and the Argonauts (1963), which features an extended fight between the actors and a group of skeletal adversaries, a considerable advance on the fight scene in Sinbad it took over four months to complete.
He returned to mythology in the 1970s with The Golden Voyage Of Sinbad (1973), Sinbad and the Eye of the Tiger (1977), and the last film to show his miniature work, Clash of the Titans (1981).
Despite his pioneering work he was not rewarded by the film community until 1992 when he was given a honorary Academy Award.
See also: Hollywood Animation: The Golden Age