5 UFC fighters who might retire in 2018

#4 BJ Penn

In its infancy, mixed martial arts was perceived stereotypically as a battle for dominance between two human gorillas. And it actually was, until the likes of BJ Penn came along. Dana White attributes the ascent of the lower weight divisions to Penn and many regard him as the greatest Lightweight of all time (Khabib says "This is number one bulls***").

With a black belt in Brazilian Jiu Jitsu after just 5 years of training and becoming the first non-Brazilian in history to win the World Jiu Jitsu championships, Penn showed that his nickname "The Prodigy", was an understatement.

Penn burst on to the MMA scene when he moved up a weight class and upset the seemingly invincible 5-time Welterweight champ Matt Hughes. He then made history by winning the Lightweight championship and becoming the 2nd man in UFC history to hold belts in different weight classes. Penn holds wins over the who's who of the UFC, beating the likes of Kenny Florian, Diego Sanchez, Jens Pulver, Joe Stevenson and Sean Sherk, to name a few.

He has hinted about retiring more than once, but you don't need to read his autobiography, "Why I Fight: The belt is just an accessory", to know why he soldiers on - the man himself has emphasized his belief that he is a born fighter and continues to do it because he loves it.

Penn was inducted into the UFC Hall of Fame in 2015 by former foe Matt Hughes. The last few years haven't been kind to the once mighty Hawaiian - he's lost his last five fights and at 39, could soon be walking off into the sunset.