UFC is the undisputed leader in the world of Mixed Martial Arts. Since their first event in 1993 several of their stars have used their fame there to enter the world of professional wrestling. Recently, Brock Lesnar made the move in the other direction. The following men have fought in both the UFC and for a major American wrestling organization (WWE, WCW, TNA, or ECW). For more information about the world of MMA, make sure to check out the martial arts site on About.com.
Brock Lesnar is the only WWE Champion to make the move from the squared circle to the octagon. While many mock pro wrestlers as being fake fighters, Lesnar proved to the world that only because someone is a pro wrestler doesn't mean they don't know how to fight. In only his fourth MMA fight, Lesnar won the most prestigious title in the business, the UFC Heavyweight Championship by beating UFC Hall of Famer Randy Couture.
Dan Severn"The Beast" Dan Severn made his first UFC appearance at UFC 4 where he lost in the tournament final to Royce Gracie. By the time he reentered the octagon and won the tournament at UFC 5, he was the holder of the NWA World Championship. Severn won that title from Chris Candido in February 1995. At that time, the belt signified that he was the best independent wrestler in the country. He entered the WWE in 1988 as part of an angle where the NWA invaded the WWE and left the company a year later. His only singles match on PPV was a loss to the Rock during the semi-final round of the 1998 King of the Ring Tournament. His UFC rival, Ken Shamrock, beat the Rock in the final round to win the tournament.
Frank TriggIn the world of UFC, Trigg is most famous for losing twice to UFC Middleweight Champion Matt Hughes. Trigg appeared in TNA during 2008. He aligned himself with Kurt Angle and eventually had an MMA Match fought under amateur rules against AJ Styles at No Surrender. The match ended in a no contest following an "accidental" low blow from Trigg. The fans hated this match and verbally expressed their displeasure. Trigg hasn't appeared in TNA since.
Ken Shamrock was already a star in the UFC when he appeared as the special guest referee during the classic WrestleMania 13 battle between Steve Austin and Bret Hart. From 1997 - 1999, Shamrock was a successful wrestler in the WWE and won the 1988 King of the Ring tournament, the Intercontinental Championship, and the WWE Tag Team Championship. At the very first TNA event in 2002, Shamrock won a gauntlet match to win the NWA World Championship. That title victory signified the return of the NWA Championship to national prominence.