Mighty Joe Young
This was Ray Harryhausen's first feature film, he worked on it alongside Willis (King Kong) O'Brien and several other animators. However it is claimed that Harryhausen did 80 percent of the animation for Mighty Joe and that he was responsible for the personality of the giant ape on the screen.
"In spite of the similarities between this film and KING KONG, Mighty Joe Young is a fantasy film of it's own right. Ernest Schoedsack and Merian Cooper worked together on this picture as they had on KONG and Willis O'Brien was brought in to supervise the special effects for the film. There was a very long, two-year period of production for MIGHTY JOE YOUNG, during which time a young Ray Harryhausen got to see O'Bie at work through the pre-production period and design stages all the way through the animation photography. Ray and O'Bie worked together designing the first armature of JOE basing it on the actual skeleton of a real gorilla. Marcel Delgado was then brought in to build up the armature with foam rubber, dental dam and cotton. Finally George Lofgren, a taxidermist, fashioned the fur for JOE devising a new process to rubberize the fur thereby avoiding the problems they had experienced with KING KONG which cause Kong fur to continually move every time an animator touched it." - quote source.
This page has a great selection of images related to the production of Mighty Joe Young, including pics of the stop motion armature for the ape.
There is an excellent page with poster, screenshots, trailer and additional info on the film at The Seventh Voyage.com