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.Recognized for his role in the resurgence of the UFC Lightweight division, Sherk became the first UFC Lightweight Champion since the division was re-introduced by the UFC in 2006. He successfully defended the UFC Lightweight Championship against Hermes Franca at UFC 73, after winning the title in a Fight of the Night award winning performance against Kenny Florian at UFC 64. Sherk is noted to have taken part in some of the most important fights in the UFC's lightweight division, where he is considered to be one of the greatest lightweight competitors of his era.