Harryhausen was born in Los Angeles in 1920 and was heavily inspired by the original, 1933 version of King Kong. Willis O'Brien, the animator on King Kong, met with the teenage Harryhausen and critiqued his model work. Harryhausen later befriended the SF author Ray Bradbury and the famous SFF and horror 'superfan' Forrest J. Ackerman in the late 1930s. During the Second World War he worked as a camera assistant on training films, working under Franz Capra (the later director of It's a Wonderful Life). Harryhausen's first work was assisting O'Brien on the original Mighty Joe Young in 1949 and ended up animating a lot of the film himself. His first solo effects work was on Beast from 50,000 Fathoms (1953).
In 1963 Harryhausen worked on the film that arguably defined his career, Jason and the Argonauts. Of particular note was a sequence where Sinbad and his crew fight off an army of stop motion-animated skeletons. The sequence is cited by many later directors and effects pioneers as being a huge influence on their careers, including Tim Burton, Nick Park, James Cameron, Stephen Spielberg, George Lucas and Guillermo Del Toro. Lucas has even said that without Harryhausen's work, he doubts Star Wars would have been made.
Harryhausen's last major film was the 1981 movie Clash of the Titans, starring Laurence Olivier. Harryhausen semi-retired after the movie was released, though some other film-makers did help him complete a long-gestating project in 2002.
Amongst the more random tributes to Harryhausen is the 2007 debut single from the band, the Hoosiers, 'Worried About Ray', which was written as a tribute to him (complete with a gorgon's head in the fridge in the official music video).
Sad news. Harryhausen was a giant in the world of special effects and his work remains highly impressive.