John Wayne Gacy was an American serial killer and sex offender who raped, tortured, and murdered at least 33 young men and boys in Norwood Park Township, near Chicago, Illinois. He became known as the "Killer Clown" due to his public performances as a clown prior to the discovery of his crimes. Gacy was sentenced to death on March 13, 1980, and was executed by lethal injection at Stateville Correctional Center on May 10, 1994.

In 1978, after one of Gacys victims, Robert Piest, was reported missing, police learned that Gacy was the last person known to have seen him. After obtaining a search warrant, police discovered the bodies of 29 boys and young men in or near Gacys house; four other bodies were found in the nearby Des Plaines River. At his trial, Gacys plea of innocent by reason of insanity was supported by the testimony of several psychologists, who diagnosed him as schizophrenic, but was ultimately rejected by the jury.

In prison, Gacy actively studied law at the Menard Correctional Center in Chester, Illinois, and continued to maintain that at least 28 of the murders had been committed by employees who had keys to his house. However, he was executed on May 10, 1994, at the age of 52.