In less than 20 years, the UFC has grown into one of the most watched sporting organisations in the world, commanding a global audience of hundreds of millions.
In that time the promotion has gone through several incarnations, throwing up era-defining champions which now litter its Hall of Fame.
As the sport of mixed martial arts has evolved, so, too, have its fighters, and each one of this list of 15 brought something new to the table to bring his skill up among the greatest champions the UFC has ever known.