Sean Keith Sherk (born August 5, 1973) is a retired American mixed martial artist and former UFC Lightweight Champion. Sherk competed in the Ultimate Fighting Championship and was one of the first combatants to have been a championship competitor in multiple weight divisions (having also competed for the UFC Welterweight Championship). He was the second UFC Lightweight Champion in the organization's history after Jens Pulver vacated his title 5 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.