Sean Keith Sherk (born August 5, 1973) is a retired American mixed martial artist and former UFC Lightweight Champion.

He was the second UFC Lightweight Champion in the organization's history after Jens Pulver vacated his title five years earlier.

Sherk also spent time competing in the Japan-based organizations, PRIDE Fighting Championships and Pancrase; going undefeated in both promotions.

He holds one of the longest undefeated streaks in mixed martial arts history, with only four career losses, all to fellow-UFC Champions.

Sherk announced his official retirement from mixed martial arts competition in September 2013 having last fought three years prior.

[10] After finding Greg Nelson's Minnesota Martial Arts Academy in 1994,[11] Sherk began to practice Judo, Boxing, Shootfighting, and Muay Thai.

[12] Sherk began his mixed martial arts career in 1999, where he went on an eight-fight win streak before signing with the Ultimate Fighting Championship (UFC) in 2001.

Sherk lost by TKO,[14] but was given another fight in the UFC at UFC 59, Sherk demonstrated that he was able to stand and strike with the more documented striker in Nick Diaz as well as mixing his combination very well with his takedowns, he defeated Nick Diaz via unanimous decision.

[19] Sherk's suspension was reduced to six months after appealing his allegations on December 4, 2007, making him eligible to fight in early January 2008.

Sherk fought Tyson Griffin at UFC 90: Silva vs Cote, in a fight with title contention implications.

He was contacted by commission officer Keith Kizer and told to return to the arena immediately or face his license being revoked.

Sherk returned within the hour and provided a urinalysis and tested clean, but was still suspended 45 days for the actions.

[25] Sherk was scheduled to face Gleison Tibau at UFC 104, but was forced off the card with an injury.

[27] However, due to an injury to Tyson Griffin, Sherk was promoted to the main card to fight Jim Miller.

[30] After a 16-month hiatus, Sherk returned on September 25, 2010 at UFC 119 and defeated Evan Dunham via split decision in a bout that earned Fight of the Night honors.