Ken Kesey (September 17, 1935 – November 10, 2001) was an American novelist, essayist and countercultural figure.

He was born in La Junta, Colorado, and grew up in Springfield, Oregon, graduating from the University of Oregon in 1957. He began writing One Flew Over the Cuckoo's Nest in 1960 after completing a graduate fellowship in creative writing at Stanford University; the novel was an immediate commercial and critical success when published two years later. During this period, Kesey participated in government studies involving hallucinogenic drugs (including mescaline and LSD) to supplement his income.

After One Flew Over the Cuckoo's Nest was published, Kesey moved to nearby La Honda, California, and began hosting happenings with former colleagues from Stanford, miscellaneous bohemian and literary figures (most notably Neal Cassady) and other friends collectively known as the Merry Pranksters; these parties, known as Acid Tests, integrated the consumption of LSD with multimedia performances. He mentored the Grateful Dead (the Acid Tests' de facto house band) throughout their incipience and continued to exert a profound influence upon the group throughout their career.

Kesey's second novel, Sometimes a Great Notion—an epic account of the vicissitudes of an Oregon logging family that aspired to the modernist grandeur of William Faulkner's Yoknapatawpha saga—was a commercial success that polarized critics and readers upon its release in 1964. Kesey regarded it as his magnum opus.

In 1965, after an arrest for marijuana possession and faking suicide, Kesey was imprisoned for five months. Shortly thereafter, he returned home to the Willamette Valley and settled in Pleasant Hill, Oregon, where he maintained a secluded, family-oriented lifestyle for the rest of his life.