Record: 22-8 overall, 12-7 in the UFC
Key Wins: Wanderlei Silva (UFC 132), Yoshihiro Akiyama (UFC 116), Aaron Simpson (Ultimate Finale 11)
Key Losses: Mark Munoz (UFC 138), Brian Stann (UFC 125), Michael Bisping (UFC 89)
How he got here: After plowing through the west coast circuit with a 14-1 record, including becoming the inaugural WEC middleweight champion, Chris Leben rose to fame on season one of The Ultimate Fighter (TUF) reality TV show.
Leben didn't have as much success fighting on the show but his drunken antics and overall personality made him a star. After the show ended, he would go on a very impressive five fight winning streak in the UFC middleweight division before earning a fight against UFC newcomer Anderson Silva and obviously that didn't end well for the Oregon native.
Since the loss to Silva, Leben has gone 7-6 in the UFC middleweight division. He was close to being released from the promotion before a very impressive three fight winning streak over the likes of Jay Silva, Aaron Simpson and Yoshihiro Akiyama thrust him back into the realm of contenders.
Leben would be halted at UFC 125 via first round stoppage loss to Brian Stann but he got right back on track by knocking out MMA legend Wanderlei Silva in just 27 seconds at UFC 132. After his victory, "The Crippler" was invited to participate in the first five round non-title main event in UFC history against Mark Munoz, but he would be stopped at the end of the third round due to severe punishment taken on the ground.
After the Munoz loss, Leben was suspended for a year and put in rehab after testing positive for painkillers in his post-fight drug screening. After 13 months away from the cage, he'll finally be returning, although he'll be facing a different opponent in Derek Brunson that he was originally training for.
How he gets it done: While Leben is a hard-hitting lefty, I'd recommend changing stances for this fight. Brunson is a southpaw as well and he was susceptible to the right hand counter from "Jacare" in his last bout, which cleaned his clock pretty badly. Look for Leben to try to stay in the pocket and force Brunson to engage, which will likely leave an opening for him to respond. As we've seen in nearly all of "The Crippler's" fights, he's not afraid to take a shot to give one back.
Granted, if the left hand is there, Leben should absolutely throw it if he can find success with it. He's got one of the heaviest left hands in the middleweight division. The biggest key for Leben is to be able to throw that left hand without risking getting clinched or taken down.
Last but not least, Leben shouldn't try to do too much too fast. He's going to be anxious to be back in the cage since he's been gone for 13 months, but there's no reason to go crazy in there and risk tiring himself out considering how long it's been since he's fought. He should be a little more patient especially considering his opponent took this fight on short notice, is young, and has a very good chance of having the Octagon jitters.
Record: 9-2 overall, 0-0 in the UFC
Key Wins: Lumumba Sayers (Strikeforce: Fedor vs. Henderson)
Key Losses: Ronaldo Souza (Strikeforce: Rousey vs. Kaufman), Kendall Grove (ShoFight 20)
How he got here: Derek Brunson was a successful high school and collegiate wrestler, but he made a transition to mixed martial arts and submission grappling once his amateur athletic career was over. Training out of Renzo Gracie's gym, he competed on the east coast for his early career in MMA, stopping every one of his first six opponents inside the opening minutes of the first round.
This earned him a shot in Strikeforce, where he won his first career decision and followed it up with a war against Lumumba Sayers in which he eventually earned a late first round submission. Brunson utilized his wrestling to move to 3-0 in Strikeforce by grinding out a decision against Nate James but he experienced a pair of setbacks.
Brunson was pulled from the Columbus event earlier this year because he wore contact lenses during his fights and after laser corrective surgery, he fought outside of Strikeforce on short notice against UFC veteran Kendall Grove, losing a controversial decision.
Teaming up with Greg Jackson's gym, he battled former Strikeforce Middleweight Champion Jacare Souza and received a 41 second knockout defeat for his efforts.
Now, after four months, he'll be one of the first Strikeforce fighters to make their way to the UFC since the promotion announced it was closing its doors as he steps in for the injured Karlos Vemola to face the returning Leben.
How he gets it done: Brunson needs to remain calm. This fight is huge for him, but he has to treat it like any other bout. He showed against Grove that he can hang with fighters more experienced than him but then he was way too eager against Souza and paid for it dearly.
Brunson has some strong offensive wrestling and he absolutely needs to utilize that. Standing with Chris Leben is a bad idea unless you're a technical fighter with solid footwork and defensive tendencies. He's got a long way to go before he's got that part of his game down.
The former wrestler shouldn't waste any time in attempting to take this fight to the ground, taking a page from Jake Rosholt's playbook against Leben by shooting early and often until he can put "The Crippler" on his back. Whether it be a counter to a Leben hook or some extraordinary effort in the clinch, he needs to put Leben down and keep him there.
There's no shame in having a boring lay-and-pray win considering who he's fighting. If that's the best way to get the "W," so be it.
Fight X-Factor: There are multiple factors at play for this fight. The first is the lengthy layoff for Leben. He's had nothing but his return bout to the UFC on his mind for about the last nine months and considering some his recent financial difficulties, he's got a ton of pressure to not only win but to put on a big performance and potentially bring home a bonus. Considering the mental strain he's put himself through in the past, the pressure could definitely mount up for him.
The other factor is Brunson getting his third shot at a top middleweight. He lost a controversial decision to Grove and then was destroyed by Souza. He's had a long time to think about those last two losses and he's going to give himself a tremendous career setback if he can't pull this fight out on Saturday. Despite stepping in on short notice as an injury replacement, he's got a lot to prove as well considering his strength of opposition and his performance thus far against known middleweights.
Bottom Line: This fight could go one of two ways. It could be a ferocious stand-up battle that will likely end with a quick and violent knockout on the feet, or it could be a grind-it-out affair where Brunson slows it down, drags it out and neutralizes all of Leben's weapons. Obviously, if we get the first option, the fight could have big time bonus potential, but it also has potential to be a huge snoozer. It may not be pretty, but making the fight boo-worthy is Brunson's best shot at a victory.
Who will come out on top at UFC 155? Tell us your predictions in the comments below!