Chicago resident John Wayne Gacy (pictured above) was convicted of sexual assault in 1968, which led investigators to the shocking discovery that he was responsible for killing 33 other young men. Most of their bodies had been buried under Gacy's home, where he lured them with the promise of a construction job. He would then kidnap, sexually assault, and strangle his victims (except his first kill, whom he stabbed to death), all of which he'd occasionally do while dressed as his alter ego, "Pogo the Clown." He was given the death penalty in 1980 and was executed by lethal injection on May 10, 1994.
His actions resulted in films like Gacy, Dear Mr. Gacy, To Catch a Killer, and the 2001 documentary Serial Killers: The Real Life Hannibal Lecters, and he was rumored to have been the inspiration behind Pennywise the clown in Stephen King's It. He also appears in American Horror Story's "Devil's Night" episode.
