Willis O'Brien was an American film special effects pioneer, best known for his groundbreaking work in stop-motion animation. He gained fame for creating the visual effects for the iconic 1933 film King Kong, where he brought the giant ape to life using innovative techniques that combined live-action and animation. O'Brien's career began in the silent film era, and he contributed to several other notable films, including The Lost World (1925). His work laid the foundation for future special effects artists and influenced the development of visual effects in cinema, making him a significant figure in the history of filmmaking.