Greg Hardy is the latest NFL player to compete in mixed martial arts, even if he isn't the greatest.

When the former defensive end steps into the Octagon on Saturday for his main-card bout against Juan Adams at UFC on ESPN 4, he'll become perhaps the most prominent example yet of an NFL player who switched to MMA.

But with a 4-1 pro record against some dubious opposition, Hardy is not the crossover figure with the most MMA success.

Who are some of the others who have successfully made the transition? 

The following fighters aren't the only former NFL players to have delved into MMA, but all five either had success or generated significant attention with their crossover.

Greg Hardy

Even if you set aside Hardy's past history with domestic violence, he's still a less-than-compelling MMA prospect.

As you might expect from a heavyweight and former All-Pro defensive end, he has strength and power to burn. His hands have notched him knockouts in all four of his pro wins.

But his cardio is a question mark, as are his skills.

The UFC scoured the roster and brought in Allen Crowder for Hardy's UFC debut in January. Hardy was a massive minus-430 betting favorite, yet Crowder dismantled his famous opponent before an illegal strike from Hardy—fancy that!—ended his night in disqualification.

The former Carolina Panthers player earned a win over a noticeably tentative Dmitrii Smoliakov in his next bout, but it wasn't the kind of "shut down the haters" win Hardy and Co. might have been hoping for. 

We'll see what happens against Adams, but either way, the UFC seemingly will give Hardy plenty more chances at a second chance. 

Brock Lesnar

By one measure, Brock Lesnar is the shining star in the NFL-MMA overlapping space. He is 5-3 (1) as a pro, but he faced elite competition and had a UFC heavyweight title run.

There's a sizable asterisk here, though. His resume as a two-sport star isn't rock-solid unless you count pro wrestling as a sport.

In 2004, Lesnar put his WWE career on hold to have a proverbial cup of coffee with the Minnesota Vikings. Although his size and athleticism made him an interesting candidate, he ultimately didn't have the polish needed to be viable at football's highest level. 

Nevertheless, he spent just enough time in the NFL to warrant inclusion here.

Herschel Walker

Herschel Walker will forever be known as a football player, but his short-lived MMA run was nothing to sneeze at.

Are Greg Nagy and Scott Carson a murderer's row of opponents? Hardly. But Walker dispatched them with a third- and first-round knockout, respectively, during a short run in the defunct but well-regarded Strikeforce promotion. 

Add in the fact he was 50 years old when he made his MMA debut, and the former Dallas Cowboys running back becomes all the more impressive. It was undoubtedly a novelty, but it was one in which the central character comported himself admirably.

Brendan Schaub

For better or worse, you may recognize Brendan Schaub as a multimedia presence in today's MMA landscape.

He retired from MMA about four years ago, but he amassed a 10-5 career record, including a first-round submission of fellow crossover Matt Mitrione and victories over Gabriel Gonzaga and Mirko Cro Cop.

He was never a great fighter—he lost convincingly any time he crept too close to the white-hot center of the UFC heavyweight division—but he was a solid roster presence.

After a career at the University of Colorado, he was on the Buffalo Bills practice squad before spending time in the Arena League. In 2009, he lost to Roy Nelson in the finals of the 10th season of The Ultimate Fighter. 

Matt Mitrione

For a former defensive tackle whose NFL career was derailed by chronic foot injuries, Matt Mitrione has carved out an impressive MMA career.

Mitrione appeared in nine games for the New York Giants in 2002, and he had a short stint with the Minnesota Vikings in 2005 before making the move to MMA. 

Like Schaub, his fight career began on the 10th season of The Ultimate Fighter, where he emerged as a hard-hitting and athletic (if not overly skilled) heavyweight. Over the next seven years, he amassed a 9-5 UFC record that included three performance bonuses and wins over Derrick Lewis and Gabriel Gonzaga. 

In 2016, he moved to the Bellator cage, where he knocked out an aging Fedor Emelianenko and reached the semifinals of the promotion's heavyweight grand prix before losing to eventual champ Ryan Bader. He's now 13-6 (1) as a pro.