William Saul Kroger (April 14, 1906 – December 4, 1995) was an American physician who pioneered the use of hypnosis in medicine and was co-founder and founder of medical societies and academies dedicated to furthering psychosomatic medicine and medical hypnosis.

Though he was trained as a gynecologist/obstetrician, his contributions to the medical field cut across disciplines and specialties in the medical field, including psychiatry, psychosomatic illness and treatment, endocrinology, neurobiology and bioengineering as well as his own specialty of gynecology and obstetrics.

He is the author of the medical textbook Clinical and Experimental Hypnosis, considered to be a classic instructional aid in the use of hypnosis in medical settings, as well as co-authoring Psychosomatic Gynecology, Including Problems of Obstetrical Care and Hypnosis and Behavior Modification: Imagery Conditioning, among others.

Kroger was born in Evanston, Illinois.

Kroger's interest in hypnosis began at an early age when his father, Charles Mendel Kroger, hired a local hypnotist to generate publicity for his fur store. The hypnotist deeply hypnotized his assistant, then buried and awoke her. This inspired him to attempt to hypnotize other children in his neighborhood at age 13.

Kroger attended Northwestern University and received his pre-medical degree in 1926.

After receiving his bachelor's degree, he joined a psychoanalytic study club, which became the Chicago Institute for Psychoanalysis and underwent his own analysis.

He received his medical training at the Feinberg School of Medicine at Northwestern University, obtaining his Doctor of Medicine in 1930. He pursued his interest in psychotherapy by taking coursework and pursued an expertise in analytic concepts under the direction of Sigmund Freud's student and founder of psychosomatic medicine, Franz Alexander.