Sullivan, Harry Stack (1892-1949) was an American psychiatrist and a leader in the development of personality theory. He viewed personality as shaped by interpersonal relationships that begin at birth.

Sullivan received his M.D. degree from the Chicago College of Medicine and Surgery in 1917, after which he served as physician in the Medical Corps with a rank of first lieuteneant. In 1922, encouraged by William Alanson White, superintendent of St. Elizabeth's Hospital in Washington, D.C., Sullivan turned to a career in psychiatry and worked with the hospital's schizophrenic patients. The theories of Sigmund Freud and social psychologists George Herbert Mead and Charles H. Cooley shaped his work. Whereas Freud thought the schizophrenic was untreatable, Sullivan trained and supervised hospital attendants to administer requisite therapies. Rather than viewing personality as the outgrowth of unfulfilled or repressed infantile fantasies, Sullivan believed that personality was a direct result of one's social interactions. Moreover, he saw one's self-concept as being molded by interpersonal relationships developed over time from infancy to maturity. Schizophrenia, he thought, was an individual's defense tactic for coping with damaging early social experiences. Unlike most others, Sullivan felt the condition could be cured through proper therapy and himself had breakthrough experiences in communicating with schizophrenics.

Among many other distinctions, Sullivan was one of the founders of the Washington (D.C.) School of Psychiatry (1936) and served for a time as president of the William Alanson White Psychiatric Foundation. He also established the journal Psychiatry in 1938. A year later he served as consultant to the White House, setting up psychiatric standards for the Selective Service System. He died on Jan. 14, 1949, in Paris, on his way home from a meeting of the World Federation for Mental Health, which he helped found.