O’Brien’s first work was a short animated film he wrote, directed and animated 1915’s The Dinosaur and the Missing Link: A Prehistoric Tragedy. He would go on to make several more prehistoric themed shorts leading to 1918’s The Ghost of Slumber Mountain where he had refined his animation techniques. O’Brien fought with the film’s producer Herbert M. Dawley. Dawley cut the film from 45 or 30 minutes (depending on the source) to 11 minutes. Some of the footage has been found and restored to the current 19 minutes but the dinosaur footage is excellent and would lead O’Brien to working on The Lost World.
After The Lost World O’Brien worked on several projects that never really materialized until 1933 when O’Brien worked on King Kong. The success of King Kong lead to a sequel, the mediocre Son of Kong. O’Brien would do effects on several other films but his next big film would be a collaboration with Ray Harryhausen on 1949’s Mighty Joe Young.
O’Brien had come up with several ideas for movies like The Beast of Hollow Mountain, King Kong vs. Godzilla and The Valley of Gwangi but he never got to work on them. Some of his incomplete story ideas included War Eagles, a story about ancient vikings who rode giant eagles and fought dinosaurs. I really want to make that movie. His last couple of movies included 1957’s The Black Scorpion and 1959’s The Giant Behemoth. Willis H. O’Brien passed away in 1962 at the age of 76.