Ken O'Brien (December 19, 1915 in Montana, USA – January 17, 1990 in Ventura, California, USA) was an American animator who was hired by March 1961 as supervising animator at Arnold Gillespie's Quartet Films. Dan Gordon left Hanna-Barbera at the same time to work for the company. O'Brien had been at Disney for a number of years and was an animator on some of the most attractive cartoons ever produced by Walter Lantz (with his buddy Fred Moore in the late '40s). He animated on the stylish John Sutherland propaganda short "Destination Earth" (1956), and spent some thankless years toiling on such dreck as the TV Magoos (he joined UPA in August 1960) and "He-Man." He also worked on animatronics in the mid-'60s at WED and taught at Cal Arts. O'Brien was from Butte, Montana, spent some teenaged years in Seattle and was supporting his widowed mother on a Disney salary by 1940. He died January 17, 1990 at age 84.
His work for Disney included character animation on Pinocchio, Bambi, Make Mine Music, Song of the South, the Bongo segment of Fun and Fancy Free, the Pecos Bill segment of Melody Time, The Adventures of Ichabod and Mr. Toad, Cinderella, Alice in Wonderland, Peter Pan, Donald's Diary, Lady and the Tramp, Sleeping Beauty, the ABC Afterschool Specials episode "The Last of the Curlews", Winnie the Pooh and a Day for Eeyore, and the ABC Weekend Specials episodes "The Puppy's Great Adventure", "The Puppy's Amazing Rescue", and "P.J. Funnybunny".