In April 2002, Thorn signed with World Wrestling Entertainment (WWE).
In late April 2004, Thorn was called up to the SmackDown! brand with vignettes playing on the show announcing his new character, Mordecai, a religious Zealot-type character. During numerous promos, Mordecai claimed to be on a crusade to rid the world of sin. He consistently wore white and had blonde hair and a beard as a sign of his purity. Mordecai debuted in ring for the SmackDown! brand on May 16, 2004 during the Judgment Day pay-per-view, defeating Scotty 2 Hotty. In later appearances, Mordecai condemned the audience for their sins, and led them in prayer. In early July, however, the gimmick was dropped.
Thorn made his return in June 2006 on WWE's ECW brand as a vampire. His first appearances on ECW on Sci Fi saw him appear in several vignettes, looking into the camera and spitting blood, while remaining unnamed and unofficially known as the "ECW Vampire". The idea behind the vignettes was that Fertig was to be part of a 'vampire' faction with Gangrel and Ariel; however, the faction did not materialise on television. The vignettes later expanded to include Ariel as a tarot card reader.
Fertig's televised in-ring debut for the brand on the July 25 episode of ECW on Sci Fi, defeating Little Guido Maritato, with Ariel acting as his valet. The next week, in another vignette, Ariel revealed his name to be Kevin Thorn. Ariel then increased her ringside presence during Thorn's matches, often interfering in his matches, and Thorn began a scripted feud with Balls Mahoney. In order to counteract Ariel's interference, Mahoney began bringing in Francine as an equalizer. The two teams feuded until early October, until Francine was released by WWE. As Ariel began to feud with Kelly Kelly, Thorn became caught up in the feud and at the December to Dismember pay-per-view, Thorn and Ariel defeated Kelly and Kelly's on-screen boyfriend Mike Knox in a mixed tag team match, after Knox walked out on Kelly.
On February 6, 2007, Thorn and Ariel joined Elijah Burke, Matt Striker, and Marcus Cor Von in forming the New Breed stable, with Thorn taking on the enforcer role and describing himself as the "muscle" of the group. The New Breed immediately engaged themselves in a feud with the ECW Originals (Rob Van Dam, Tommy Dreamer, Sabu and The Sandman). Different members of the New Breeds wrestled members of the ECW originals over several weeks, leading up to WrestleMania 23. At WrestleMania, the New Breed was defeated by the ECW Originals in an 8-man tag team match, but won a rematch on the following episode of ECW. In April, CM Punk aligned himself with the New Breed after weeks of recruiting. Just two weeks later, however, Punk betrayed the New Breed and attacked Burke after a match. The following week, Burke announced a match between Thorn and Punk, but Thorn lost. After the match, Thorn quit the New Breed, as none of the other members interfered during the match to help him.
On May 18, Ariel was released by WWE. The following week, Thorn appeared by himself, with the commentators claiming that Thorn was "flying solo". After leaving Ariel, Thorn was pushed, defeating superstars such as Tommy Dreamer and Stevie Richards. His winning streak came to an end on July 3, however, when he lost to CM Punk on ECW. Thorn then began a feud with Stevie Richards, after Richards defeated Thorn in an upset on two consecutive occasions. Following this, Thorn attacked Richards backstage. He later pinned Richards in a match, but the referee reversed the decision, and awarded the match to Richards, when Thorn attacked Richards after the match. Despite this, Thorn defeated Richards the following week, and then teamed up with Elijah Burke to defeat Richards and Tommy Dreamer in a tag team match. On the September 18 episode of ECW, Thorn along with Burke, Dreamer, and Richards involved themselves in an Elimination Chase to No Mercy to face Punk. In their first match, a fatal four-way, Thorn was victorious, eliminating Richards, but was eliminated himself the following week, due to being pinned in a triple threat match.
On November 20, 2007, Thorn debuted a new look, with shorter hair and different ring attire, while defeating Nunzio. Soon after this image change, Thorn was taken off of television.