After WCW was purchased by the World Wrestling Federation (WWF) in March 2001, Moore signed a contract with

them and was assigned to the Heartland Wrestling Association (HWA), a Louisville-based WWF developmental

territory. He teamed with Karagias in HWA until Karagias was released by the WWF. Moore would make his TV debut

on the July 13, 2002 episode of Velocity.

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In 2003, after competing in the cruiserweight division for several months as a fan favorite, Moore became a villainous

acolyte of Matt Hardy, who had begun proselytizing a philosophy known as "Mattitude" and calling himself "Matt Hardy Version 1.0". Moore became a "Mattitude Follower" (abbreviated "MF'er") and started dressing like Hardy and accompanying him to ringside. Moore often lost to more physically dominant opponents or unsuccessfully attempted to help Hardy win his matches, both things that resulted in Hardy attacking Moore in order to vent his frustrations, claiming that he had "failed to comprehend [Hardy's] coaching!" Moore did, however, assist Hardy in his bid to lose several pounds in order to qualify for a WWE Cruiserweight Championship title shot, which he won when Moore came through again, this time distracting then face, Billy Kidman to enable Hardy to get the win and the title. On April 24, Crash Holly also became an MF'er. He was subordinate to Moore and, as such, was referred to as a "Moore-on". The group was short-lived, though, as Crash was released from WWE on June 30.

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Moore and Hardy continued to work together until November 17, when Hardy left SmackDown! and joined the Raw brand. As a result, Moore was a fan favorite again and Paul Heyman (SmackDown's then-general manager) decided to punish Hardy vicariously for leaving his show by forcing Moore to face a series of much larger opponents. In successive weeks, Moore was squashed by Matt Morgan, Nathan Jones, and The Big Show, before unexpectedly                                                                                           defeating A-Train in an upset victory on the December 11 episode of SmackDown!. The following week, WWE                                                                               Champion Brock Lesnar was scheduled to defend his title against a random wrestler, with the name of his                                                                                       opponent selected arbitrarily by a lottery machine. Moore was selected as Lesnar's opponent, and Lesnar                                                                                       defeated him with ease and then revealed that all the balls had borne Moore's name, with Lesnar having rigged the                                                            process in order to ensure that he would have a much smaller opponent. Immediately after the match, Moore                                                                                 and Hardcore Holly were scheduled to face A-Train and Morgan in a tag team match, with Holly gaining a title                                                                               shot if he won and being fired if he lost. Despite Moore being incapacitated, he and Holly were able to win                                                                                     the match.

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In 2004, at WrestleMania XX Moore took part in a "Cruiserweight Open" for the Cruiserweight Championship, but was eliminated by Último Dragón. His next high-profile appearance was on the July 8, 2004 episode of SmackDown!, which saw Moore wrestle under a mask as "El Gran Luchadore". Moore faced John "Bradshaw" Layfield (JBL) in the match for the WWE Championship and was initially dominated by his much larger opponent. A second Luchadore (the disguised Eddie Guerrero), however, took Moore's place, prompting Layfield to run away, thus giving Moore the victory by count out.