Despite losing his lightweight belt to Frankie Edgar, B.J. Penn is still considered one of the greatest lightweights of all time. However, Edgar has already made a case at surpassing him with back-to-back wins over the former champion and two title defenses.
One of the most competitive divisions in the sport, the lightweight division has never seen a UFC champion who defended their title more than three time consecutively.
This makes it hard to differentiate which lightweights have been the greatest ever, but that won't stop us at Bleacher Report from attempting to do just that.
Having fought for the UFC lightweight title on two occasions, Kenny Florian has long been considered one of the best fighters in the division.
Although Florian has been unable to reach the top of the mountain, his only UFC losses at lightweight have come against Sean Sherk, B.J. Penn and Gray Maynard.
Despite all his success at lightweight, Florian has recently decided to leave the division in an attempt to make a run at the UFC Featherweight Championship.
In addition to a win over Kenny Florian, Gray Maynard has also gotten the better of current UFC Lightweight Champion Frankie Edgar in their two fight series.
If Maynard is able to walk away with a second win over Edgar in their upcoming third meeting, it would go a long way toward validating his position on this list.
Undefeated in 12 career fights, Maynard has also beaten Jim Miller, Nate Diaz and Roger Huerta.
Since joining Bellator in 2009, lightweight champion Eddie Alvarez has been unstoppable. During his seven fights with the organization, Alvarez has defeated Toby Imada, Josh Neer, ROger Huerta and Pat Curran.
Prior to joining Bellator, Alvarez also scored wins over Tatsuya Kawajiri and Joachim Hansen. However, he was also defeated by Shinya Aoki and Nick Thomson.
With Zuffa's purchase of Strikeforce, Bellator is beginning to run out of options for worthy competitors for Alvarez.
After spending the majority of his career at welterweight, Sean Sherk made and extremely successful drop to lightweight in 2006.
In his first fight at 155 pounds, Sherk defeated Kenny Florian to become the first UFC Lightweight Champion in four years.
Sherk was then forced to vacate his belt after testing positive for steroids following his first title defense against Hermes Franca.
Upon his return from suspension for the positive steroids test, Sherk once again fought for the lightweight belt. However, he was defeated by B.J. Penn and has not earned another title shot since.
Approaching the twilight of his career, Takanori Gomi has been disappointing since joining the UFC.
However, that shouldn't take away from Gomi's accomplishments earlier in his career. Gomi has had several notable victories and was the only lightweight champion in Pride history. Gomi was also a 154-pound champion with Shooto.
Throughout his career, Gomi has defeated lightweight greats such as Jens Pulver, Tatsuya Kawajiri, Hayato Sakurai and Marcus Aurelio.
During his illustrious career, Shinya Aoki has held lightweight titles for Dream and WAMMA. Aoki has also fought for the Strikeforce Lightweight Championship.
Aoki has earned wins over some of the best lightweights in the history of the sport during his career. Some of Aoki's victims include Joachim Hansen, Caol Uno, Eddie Alvarez, Tatsuya Kawajiri and Marcus Aurelio.
Aoki's only lightweight loss that has gone unavenged was his loss in a title fight against Gilbert Melendez.
Jens Pulver hasn't done his legacy any favors by continuing to fight over the last few years, but he remains one of the best lightweights of all time.
The inaugural UFC Lightweight Champion, Pulver defeated B.J. Penn, Caol Uno and Dennis Hallman during the prime of his career.
Penn is the only fighter to defend the UFC lightweight belt more times than Pulver.
During his 21 professional fights, Gilbert Melendez does not have a loss on his record that he hasn't avenged.
With two wins over Tatsuya Kawajiri and a win against Shinya Aoki, Gilbert Melendez is the greatest lightweight to never fight in the UFC. However, his time in the Octagon could be coming sooner rather than later.
Melendez is a two-time Strikeforce Lightweight Champion and former WEC Lightweight Champion.
A case could be made for Frankie Edgar as the greatest lightweight ever. However, his inability to defeat Gray Maynard has him at number two on this list for now.
Edgar holds wins over B.J. Penn, Sean Sherk and Jim Miller.
While Edgar is only one win away from matching Penn's record of three consecutive lightweight title defenses, he will need a more decisive defense against Maynard than he had earned with a draw in his last fight in order to surpass Penn..
With wins against nearly half of the fighters on this list, B.J. Penn is the greatest lightweight in MMA history.
Penn holds the record for most consecutive UFC Lightweight Championship defenses with three and some would argue that he should have had a fourth after his first fight with Edgar.
Over the course of his lightweight career, Penn has defeated Caol Uno, Takanori Gomi, Jens Pulver, Sean Sherk, Kenny Florian and Diego Sanchez.