Ken Kesey was an American author and Merry Prankster who is best known for his novel 'One Flew Over the Cuckoo's Nest'. He was also a part of the 1960s counterculture movement, and was known for his use of psychedelic drugs. He was a leader of the 'Merry Pranksters', a group of people who traveled across the United States in a painted school bus, engaging in various pranks and experiments. Kesey was also a key figure in the development of the psychedelic music scene in San Francisco.