 In 2006 , <unk> pursued a career in mixed martial arts . He signed with Hero 's and won his first fight , against <unk> @-@ <unk> Kim , in June 2007 . He then signed with the Ultimate Fighting Championship ( <unk> ) the following October . <unk> lost in his <unk> debut against Frank <unk> and then won his second fight against Heath <unk> . In November 2008 , <unk> defeated Randy <unk> to become the <unk> Heavyweight Champion . Shortly after a successful title defense in a rematch with <unk> , <unk> was sidelined due to <unk> . He would return at <unk> 116 to defeat Interim <unk> Heavyweight Champion Shane <unk> and <unk> the heavyweight championships , becoming the <unk> Heavyweight Champion . <unk> then lost the championship to Cain <unk> at <unk> 121 . In 2011 , he was once again sidelined due to <unk> and underwent surgery . <unk> returned at <unk> 141 in December , losing to <unk> <unk> and promptly retiring from <unk> . <unk> was a box office sensation in <unk> . He took part in a few of the best selling pay @-@ per @-@ views in <unk> history , including <unk> 100 and <unk> 200 . 
