Claim: Brock Lesnar lost a fight against a K-1 kickboxer.

Brock Edward Lesnar -LRB- -LSB- ˈlɛznər -RSB- born July 12 , 1977 -RRB- is an American professional wrestler and former mixed martial artist , amateur wrestler , and professional American football player . He is signed with WWE , where he performs on the Raw brand and is the current WWE Universal Champion in his first reign .   After his successful amateur wrestling career at Bismarck State College and the University of Minnesota , Lesnar signed with WWE -LRB- then the World Wrestling Federation -RRB- in 2000 . He was assigned to its developmental promotion Ohio Valley Wrestling -LRB- OVW -RRB- , where he was a three-time OVW Southern Tag Team Champion with Shelton Benjamin . After debuting on WWE 's main roster in 2002 , he won the WWE Championship on three separate occasions with victories over The Rock and Kurt Angle -LRB- twice -RRB- . Lesnar won the then WWE Undisputed Championship five months after his main roster debut at the age of 25 , becoming the youngest champion in the title 's history . He was also the 2002 King of the Ring and the 2003 Royal Rumble winner , making him the youngest King of the Ring and Royal Rumble winner as well . Following his match with Goldberg at WrestleMania XX , Lesnar left the WWE and pursued a career in the National Football League -LRB- NFL -RRB- . He was named a defensive tackle for the Minnesota Vikings , but was cut prior to the start of the 2004 -- 2005 season . In 2005 , Lesnar returned to professional wrestling and signed with New Japan Pro-Wrestling -LRB- NJPW -RRB- , where he won the IWGP Heavyweight Championship in his first match . After a contractual dispute with NJPW , he also wrestled as IWGP Heavyweight Champion in the Inoki Genome Federation -LRB- IGF -RRB- .   In 2006 , Lesnar pursued a career in mixed martial arts -LRB- MMA -RRB- , as he signed with Hero 's and won his first fight , against Min-Soo Kim , in June 2007 . He then signed with the Ultimate Fighting Championship -LRB- UFC -RRB- the following October . Lesnar lost in his UFC debut against Frank Mir and then won his second fight against Heath Herring . In November 2008 , Lesnar defeated Randy Couture to become the UFC Heavyweight Champion . Shortly after a successful title defense in a rematch with Mir , Lesnar was sidelined due to diverticulitis . He would return at UFC 116 to defeat Interim UFC Heavyweight Champion Shane Carwin and unify the heavyweight championships , becoming the Undisputed Heavyweight Champion in the process . Lesnar then lost the championship to Cain Velasquez at UFC 121 . In 2011 , he was once again sidelined due to diverticulitis and underwent surgery . Lesnar returned at UFC 141 in December , losing to Alistair Overeem and promptly retiring from MMA . Lesnar was a box office sensation in UFC , as he took part in a some of the best selling pay-per-view events in UFC history , including UFC 100 and UFC 116 .   In April 2012 , Lesnar once again returned to professional wrestling , rejoining WWE after an eight-year hiatus . Two years later , at WrestleMania XXX , Lesnar defeated The Undertaker to end his undefeated streak at WrestleMania . He achieved world champion status twice since his return , having won the then WWE World Heavyweight Championship in 2014 and the WWE Universal Championship in 2017 . Lesnar has been managed by Paul Heyman throughout the majority of his professional wrestling career .   In June 2016 at UFC 199 , the UFC announced that Lesnar would return to MMA to fight at UFC 200 . His opponent was later revealed to be Mark Hunt . Lesnar would defeat Hunt via unanimous decision . However , after Lesnar tested positive for clomiphene , a banned substance on the UFC 's anti-doping policy , he was suspended from competing in the UFC by the Nevada State Athletic Commission for one year , fined $ 250,000 and his victory over Hunt was overturned to a no-contest . Lesnar then retired from MMA for a second time in 2017 .   Lesnar is a five-time world champion in WWE , a one-time heavyweight champion in the UFC , a one-time heavyweight champion in NJPW , and a one-time heavyweight wrestling champion in the NCAA , the only person in history to win a championship in each of those organizations . He has headlined numerous pay-per-view events for both the WWE and UFC , including WrestleMania XIX , WrestleMania 31 , UFC 100 and UFC 116 . In 2015 , an ESPN.com article referred to Lesnar as `` the most accomplished athlete in professional wrestling history '' .