Due to Brock's size, look and athletic background he was high on the radar of then WWE Head of Talent relations Jim Ross. Hired by WWE in 2000, Brock trained in Florida Championship Wrestling before rapidly debuting on Monday Night Raw in 2002. Brock was an extremely fast learner in the ring, and during his relatively short tenure in WWE he became widely regarded as one of the greatest "big men" wrestling has ever seen. He had memorable feuds were with The Rock, Kurt Angle, The Undertaker, John Cena, and Big Show. It was during this time with that Brock met his wife Rena Mero (WWE Diva Sable).
Being on the road for the majority of the year at the forefront of the WWE promotional machine was a far cry from his upbringing in South Dakota, and the pressure took its toll. Brock left WWE shortly after his Wrestlemania XX match with the also soon-to-be-leaving Bill Goldberg, a fact not lost on the fans in attendance who were openly hostile towards the two.
In 2004 Brock tried out for the NFL, where he was a late cut for the Minnesota Vikings. As an athlete Lesnar was exceptionally impressive, but did not have the raw skills he would have developed by playing football at college level. Lesnar was offered and declined a place in the European NFL. He appeared as a playable character in Madden 06.
In 2007 Brock defeated Kim Min-Soo of South Korea in his very first MMA fight, eventually being signed by the UFC the following year. Brock's years of international TV exposure, coupled with his genuine athletic background in amateur wrestling, made him a interesting prospect within the organisation, and garnered significant interest throughout the MMA and wrestling communities.
Brock lost his debut UFC match against Frank Mir at UFC 81, losing by kneebar in the first round. Prior to the submission Lesnar was dominating the fight, knocking Mir down numerous times and unleashing devastating ground and pound offence.
After being scheduled to fight ageing UFC hall of famer Mark Coleman, Lesnar was matched against former Pride star Heath Herring at UFC 82. Bad blood developed between the two, with Heath Herring and his camp feeling insulted that their fighter was being drafted against a mere "WWE wrestler". Within seconds of the fight Brock fractured Herring's orbital bone with a straight right hand and preceded to use his wrestling, positional dominance, and ground and pound to win a one sided unanimous decision victory. Heath has not fought since.
Brock was beginning to be seen as a legitimate mixed martial artist and, perhaps more importantly a legitimate star, and so was chosen by UFC hall of famer Randy Couture as his return opponent following a year long hiatus from the UFC. The then Heavyweight Champion, Randy was known for his excellent Greco-Roman wrestling skills and was seen as a major step up in competition for Lesnar. At UFC 91, Lesnar defeated Couture via second round TKO (due to ground and pound), to win the UFC Heavyweight Championship.
At UFC 100, Brock defended his title against Frank Mir in a rematch of their 2008 bout. With both fighters giving tremendous performances in the build up to this match, UFC 100 became one of the biggest grossing pay per views in cable television history. Wary of Frank's Jui-Jitsu and it's effectiveness in their previous fight, Brock looked to closely control Frank's body on the ground, leaving little space for Frank to execute possible submissions. Brock won via second round ground and pound, leaving Frank's face a crimson mask. Brock created controversy after the fight when he continued to talk trash a defeated Mir and joked on camera about preferring an alternative product to an official UFC sponsor; a joke he has since apologised for.
Lesnar was slated to face undefeated Shane Carwin at UFC 106 but on October 26, 2009 it was announced that due to a "prolonged illness" the fight was postponed. Forrest Griffin vs. Tito Ortiz 2 was moved to the main event of UFC 106. This illness was later revealed to be a severe case of diverticulitis, an inflammation and (in this case) perforation of his intestine.
Lesnar was hospitalised for nearly two weeks and faced major surgery and likely forced retirement from athletic competition.
After months of speculation on whether or not Lesnar would ever return to the octagon Lesnar announced that his illness had healed without requiring surgery, and that he would return in the summer of 2010 to defend the championship against Shane Carwin at UFC on July 3rd 2010. During Lesnar's hiatus from the sport, Carwin had defeated Frank Mir to be crown the Interim UFC Heavyweight Champion, and this fight would unify the two titles into one.
Known as a one of the hardest punchers in sport, Carwin landed a clean uppercut early in the first round which rocked Lesnar. Carwin proceeded to unleash a devastating ground and pound assault. Lesnar managed to cover up and move enough for the fight not to be stopped, and managed to force his way back onto his feet late in the round. Showing previously unproven resilience, Lesnar took a tired Carwin to the mat early in the second round, soon securing a neck choke for a submission victory.
Brock is known for being a deeply private person, but reveals a larger than life persona when it comes to promoting and building interest in his fights. This persona is likely to have been influenced by Brock's relationship with former ECW promoter Paul Heyman, who became friends with Brock during his time with WWE.
Brock's household has no mobile phone, no internet, and only has cable TV in order for him to be able to "watch the hunting and fishing channels". He also has a distinctive tattoo of a grenade-handled dagger on his chest, one that deserves to be ranked highly in any list of crappy tattoos.
Brock Lesnar lost his UFC Championship belt on October 23, 2010 in a first round defeat (4 mins 12 sec.TKO ) to Cain Velasquez.