Gillberg debuted in 1992 with Barry Hardy as The Executioners, and took part in a 40-man battle royal won by Tatanka. The Executioners split in early 1994 and Hardy left the company on April 18. Gillberg then began competing under his real name as an enhancement talent before also leaving the company soon after.
In 1998, Gillberg made his return to the World Wrestling Federation at Survivor Series as Mankind's mystery opponent. Vince McMahon seemingly facilitated Mankind's route to victory in a tournament for the vacant WWF Championship as he appeared to be McMahon's favorite to win. Before Gillberg made his entrance, McMahon built up the suspense by referring to him as a wrestler with a win/loss record that no other wrestler could match. Although the statement was thought to indicate that Mankind's opponent won more than lost in his career, the exact opposite was true and Gillberg was squashed by Mankind. He later joined the J.O.B. Squad with Al Snow, Scorpio, and Bob Holly.
During this time, Gillberg became notable for "ending" Marc Mero's career when Mero challenged him to a match, announcing to the crowd that he would retire from wrestling if he could not beat Gillberg. Gillberg won the match with some help from the J.O.B. Squad and Mero left the WWF, although he did not legitimately retire as promised.
On November 17, 1998, Gillberg won the Light Heavyweight Championship after defeating Christian on Raw is War. Shortly after, he began to really parody Bill Goldberg.
Gillberg made his Royal Rumble debut in 1999, but was immediately eliminated by Edge. Gillberg's only victory came on the February 15, 1999 edition of Raw is War, when he defeated Goldust with help from former J.O.B. Squad member Blue Meanie, who was feuding with Goldust at the time. While he still came to the ring with the belt, the Light Heavyweight Championship was all but forgotten as Gillberg seldom defended the title on television or at house shows. After being off of WWF television for several months, Gillberg returned on the February 13, 2000 episode of Sunday Night Heat for one final match in order to lose the championship to the debuting Essa Rios. Upon losing the title, Gillberg's reign ended at 15 months, making him the longest reigning Light Heavyweight Champion in WWF history.
When Bill Goldberg came to WWE in 2003, his first feud was against The Rock, who on the April 21, 2003 edition of Raw brought in Gillberg to mock Goldberg. After beating up The Rock's security guards, who were trying to apprehend him for interrupting a concert "dedicated" to him, Gillberg attacked Goldberg with an amazing reaction from the fans, and after Goldberg was choking him he was attacked by The Rock from behind. The Rock and Gillberg then quickly ran out of the arena to avoid any further conflict.
On December 10, 2007, Gillberg, now sporting two new tattoos on his left deltoid, returned to WWE television for the 15th Anniversary of Raw. During the show, he participated in a 15-Man Battle Royal against fourteen other former Raw wrestlers, but was the first man eliminated only a few seconds into the match by every other competitor.