William Stanley Milligan (February 14, 1955 – December 12, 2014), also known as The Campus Rapist, was an American who was the subject of a highly publicized court case in Ohio in the late 1970s. After having committed several felonies including armed robbery, he was arrested for three rapes on the campus of Ohio State University. In the course of preparing his defense, psychologists diagnosed Milligan with dissociative identity disorder. His lawyers pleaded insanity, claiming that two of his alternate personalities committed the crimes without Milligan being aware of it. He was the first person diagnosed with dissociative identity disorder to raise such a defense, and the first acquitted of a major crime for this reason, instead spending a decade in psychiatric hospitals.

Milligan's life story was popularized by Daniel Keyes's award-winning non-fiction book The Minds of Billy Milligan.