Willis Harold O'Brien, known as Obie O'Brien, was an American motion picture special effects and stop-motion animation pioneer, who according to ASIFA-Hollywood "was responsible for some of the best-known images in cinema history," and is best remembered for his work on The Lost World (1925), King Kong (1933), The Last Days of Pompeii (1935) and Mighty Joe Young (1949), for which he won the 1950 Academy Award for Best Visual Effects.

Stop motion is an animated filmmaking technique in which objects are physically manipulated in small increments between individually photographed frames so that they will appear to exhibit independent motion or change when the series of frames is played back. Any kind of object can thus be animated, but puppets with movable joints or plasticine figures are most commonly used. Puppets, models or clay figures built around an armature are used in model animation. Stop motion with live actors is often referred to as pixilation. Stop motion of flat materials such as paper, fabrics or photographs is usually called cutout animation.