Fatu debuted on the April 3, 2006 episode of Raw with a new gimmick similar to that of Kamala and The Headshrinkers. Now called Umaga, the same name of the final and most painful part of the Samoan tattooing process, meaning "the end", he was depicted as a destructive savage who could only be controlled by his manager, Armando Alejandro Estrada. The pair started out feuding with Ric Flair, whom Estrada interrupted in the middle of a promo to tell how much of a fan of his he used to be, but that now he was old and needed to retire. It was in offering the fans a new "hero" to watch that he introduced Umaga, who proceeded to beat down Flair. For the next few weeks Umaga participated in squash matches, destroying various jobbers, until he dispatched Flair at Backlash at the end of the month.
The summer months saw Umaga winning matches against the majority of the Raw roster, including the likes of Triple H, Shawn Michaels, and John Cena, who at the time was still WWE Champion. His next actual feud started at August's SummerSlam, where he was supposed to be an enforcer on behalf of The McMahons (the heel gimmicks of Vince and Shane) during their match against D-Generation X (Shawn Michaels and Triple H), only to be attacked by then face, Kane as he made his entrance. Kane and Umaga feuded for the next two months until Umaga won a Loser Leaves Raw match, sending Kane off of the brand. After being separated by different brands, Umaga and Kane had one final match at Cyber Sunday where Umaga again defeated Kane after fans selected him over Chris Benoit and The Sandman to be Umaga's opponent for the night.
Umaga, having still not been pinned in the WWE, was then deemed the number one contender for the WWE Championship and placed into a feud with then-champion John Cena over the title. Cena retained his belt at the New Year's Revolution pay-per-view by pinning Umaga with a roll-up, officially ending his streak, which had lasted 34 televised matches and spanned from his re-debut in April 2006 to January 2007. In that time Umaga was never pinned or made to submit on television, although he did lose two matches by disqualification and another went to a double countout. For the rest of the month, Estrada played down Cena's victory, claiming it was a fluke, until a Last Man Standing rematch was signed for the next pay-per-view, the Royal Rumble. On an episode of Raw between the two pay-per-views, Umaga attacked Cena causing a worked injury to his spleen and putting the match in jeopardy. Cena kayfabe refused a medical exam, the results of which could cause him to forfeit his title, and then defeated Umaga by submission, wrapping a loosened ring rope around his neck during an STFU.
Though he was out of the world title picture, Umaga was named Vince McMahon's "representative" for the WrestleMania 23 "Battle of the Billionaires" with Donald Trump. Immediately after choosing Umaga, McMahon "granted" him a match against the Intercontinental Champion, Jeff Hardy, which he won handedly to take the title. After Bobby Lashley was named Trump's representative, the two began a feud which lasted even beyond WrestleMania. Despite Umaga losing in the "Battle of the Billionaires" hair versus hair match and causing Vince McMahon to get his head shaved, the McMahons (Vince and Shane) continued to second him to the ring. Two weeks after WrestleMania, Lashley interfered in a match and helped a planted fan, Santino Marella, defeat Umaga for the Intercontinental title. At the April 29 Backlash event, the team of Umaga, Vince, and Shane McMahon wrestled Bobby Lashley for his ECW World Championship in a Handicap match, winning the title for Vince.
Umaga would continue to be involved with the Lashley/McMahon feud, competing at Judgment Day in the return match for the ECW Championship, which was once again a Handicap Match with the McMahons along with Umaga taking on Bobby Lashley. The feud culminated at One Night Stand, with Umaga aiding The McMahons in defending the ECW Championship against Bobby Lashley in a Street Fight Match, which Umaga and The McMahons lost.In June, Umaga was re-entered into a feud with Marella, the man who won his Intercontinental Championship earlier in April. When they met at the Vengeance pay-per-view, Umaga was solidly in control of the match, but lost by disqualification when he disregarded the referees instructions and continued to punch Marella. In a rematch on July 2, Umaga beat Marella to win the Intercontinental Title back. Not long after, he seemingly started a face turn, joining forces with John Cena against Carlito and Randy Orton. After defeating both Kennedy and Carlito in a triple threat match at SummerSlam to retain his Intercontinental Title, Umaga interrupted a Raw match between Kennedy and a returning Jeff Hardy, assaulting Hardy and leaving him lying in the ring thus turning heel again. One week later, on the September 3 Raw, Umaga lost the Intercontinental title to Hardy in a singles match. Later that night, he teamed with Carlito in a handicap match against Triple H, after which Triple H struck him several times with his signature sledgehammer, injuring him.  He was given a match against Triple H at No Mercy, which was changed to a title match for the WWE Championship during the event when Triple H won the title earlier that night. Fatu was defeated by Triple H in their match. At Survivor Series his team of MVP, Mr. Kennedy, Finlay and Big Daddy V lost to Triple H's team. Coming up to WrestleMania XXIV, Fatu started feuding with Batista, but he lost to him at WrestleMania. Upon Jeff Hardy's return, William Regal sent Umaga into the ring to "punish" Jeff, thus reigniting the feud between them. Umaga would go on to face Jeff Hardy at WWE One Night Stand in a Falls Count Anywhere Match, which Umaga lost.
On June 23, 2008, Umaga was drafted from the Raw brand to the SmackDown brand, as a part of the 2008 WWE Draft. After having a short lived rivalry with Mr. Kennedy and The Big Show, Fatu suffered a torn PCL at a SmackDown live event in Johnson City, Tennessee on August 2 during a match with Jeff Hardy.
On the January 30, 2009 episode of SmackDown, Umaga returned to action with his unstoppable persona and won his return match against Jimmy Wang Yang. Umaga then suffered his first defeat since his return by losing to Triple H by disqualification, after Triple H was attacked by The Legacy (Randy Orton, Ted DiBiase, Jr. and Cody Rhodes). After a short hiatus, he returned on the May 1, 2009 episode of SmackDown, attacking CM Punk on multiple occasions, repeatedly interrupting Punk's attempts to cash in his Money in the Bank briefcase. At Judgment Day, Umaga defeated Punk, and on the May 22 episode of SmackDown, he spoke in English for the first time under the Umaga gimmick, when he challenged Punk to a Samoan strap match. At Extreme Rules(which was his final match in the WWE) Umaga lost to Punk, and Punk later cashed in the Money In the Bank later that night to win the World Heavyweight Championship from Jeff Hardy.
On June 8, 2009, Umaga was released from his WWE contract. It was later revealed that this was due to violation of the Wellness Policy; even though this was only his second failure, his refusal to enter rehabilitation led to his premature dismissal.
On December 4, 2009, Umaga Died From A Heart Attack At The Age Of 36.