Damien, under the name Mondo Kleen, debuted in WWF at a live event on October 2, 1992 in a losing effort to Jeff Jarrett. On the October 12 episode of Superstars of Wrestling, He made his televised in-ring debut as Damien Demento, a villainous character who hailed from "The Outer Reaches of Your Mind" and showed mentally disturbed behavior. He then proceeded to defeat Steve May in his televised debut match. On the October 28 episode of Wrestling Challenge, he defeated Jim Brunzell.
Demento was in the main event of the debut episode of Monday Night Raw on January 11, 1993, losing to The Undertaker. Demento made his only pay-per-view appearance at Royal Rumble as a participant in the 1993 Royal Rumble match and lasted over twelve minutes before being eliminated by Carlos Colón. After this, Demento competed almost solely on house shows before leaving the WWF in October 1993.