After The Bushwhackers helped forward a tape of Theis performing an interview, the World Wrestling Federation signed him to a contract. Theis, under his Mondo Kleen ring name, 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, Theis made his televised debut under the repackaged ring name and gimmick of "Damien Demento", a villainouscharacter 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. He also appeared at UK Rampage '93, where he lost to Bob Backlund. After this, Demento competed almost solely on house shows before leaving the WWF in October 1993.
After a stint on the East Coast independent circuit, Theis retired from wrestling in 1994. Under his Damien Demento ring name, he made a short return to wrestling on November 8, 2008, where he defeated The Musketeer in a match for the New York-based World of Unpredictable Wrestling. A month later they had a rematch in which Demento was on the losing end. He made another return to the squared circle in September 24, 2011. This time wrestling as "Mondo Kleen", he defeated Steven Person in a steel cage match at a show that WUW promoted for the Dumbo Arts Festival. On October 29, 2011, Damien Demento defeated long time WUW Trophy Champion "Izzy" Israel Joffe at the WUW October show at Gleason's gym to win the WUW Trophy Championship. On December 10, 2011, Israel Joffe defeated Damien Demento at the WUW December show at Gleason's gym. In 2014, Demento made a few appearances for World Wrestling Organization.
Partial filmography
Die Hard with a Vengeance - Erik
Personal life
Theis originally wanted to become a football player, he majored in art at Wagner College while on a football scholarship and later on had a tryout with the Jets but did not make the team. Theis instead began training for a career in professional wrestling. He cites King Curtis Iaukea as his inspiration for becoming a wrestler. After retiring from professional wrestling, he began working as an artist and a sculptor.