He had defeated Paulo Filho at WEC 36 -- a non-title bout due to the Brazilian's failure to make weight -- and a month later, the 185-pound division was absorbed into the larger UFC.
The success Sonnen found in the now defunct promotion saw him re-enter the Octagon as a potential contender for Anderson Silva. The West Linn, OR native had previously fought for the UFC but was cut after dropping two out of three bouts.
In the time between Octagon stints, Sonnen kept busy with a couple of different organizations including earning four straight wins for bodogFIGHT before signing to WEC and fighting once again under the Zuffa umbrella.
But things didn't go quit as planned for the prodigal son in his re-debut.
Sonnen locked horns with Demian Maia and was quickly taken down and submitted. He bounced back with a win over Dan Miller and followed that victory up with a second against the tough Yushin Okami. For some perspective, the Japanese fighter had lost only twice in the previous five years leading up to his bout with Sonnen; he came up short against Jake Shields in a 175-pound tournament and against Rich Franklin at UFC 72.
The pair of triumphs put "The American Gangster" on a collision course with Nate Marquardt who was gunning for a second crack at Silva after failing to usurp the Brazilian at UFC 73: "Stacked." Going into his bout with Sonnen, "The Great" was riding the momentum of three consecutive stoppage victories including a brutal 21 second knockout over the aforementioned Maia.
The two met at UFC 109 with a title shot on the line.
Before Sonnen once again does battle with "The Spider" at UFC 148: "Silva vs. Sonnen II," we'll take a look at the bout in which the American earned his opportunity to face the champion. This victory ended up putting him and Silva inside the Octagon for the first time.
Not even a minute into the fight and Sonnen has Marquardt on his back. "The American Gangster" opens the bout like a fireball, immediately pressuring his opponent with striking and dirty boxing before dumping "The Great" onto the mat.
As he does, however, the former title challenger sinks in a guillotine. Submission defense has always been Sonnen's Achilles' heel and the thought of the Team Quest fighter losing another fight thanks to it immediately jumps to the forefront of everyone's mind.
He survives the attempt, however, and begins to rain down punches and elbows. Marquardt manages to get to his feet and throws a flying knee which partially connects but Sonnen uses the opportunity to get his opponent back onto the mat.
They scramble on the canvas and again "The American Gangster" winds up on top. A flurry of activity from Sonnen sees punch after punch and elbow after elbow land against Marquardt's skull.
To begin the second round, Sonnen makes a beeline for his opponent and wastes no time in securing a takedown. Fighting off a kimura attempt from Marquardt, the Team Quest fighter continues the onslaught he began in the opening heat.
A dagger-like elbow from "The Great" catches Sonnen's brow and his forehead opens up like a geyser. Answering back, Sonnen lands a huge punch from above but within seconds, however, the Octagon looks more like a crime scene than a sports venue.
With his own blood pouring all over his opponent, Sonnen takes Marquardt's back and continues his domination. A last ditch effort from "The Great" gets him back to his feet but it's fleeting as Sonnen almost immediately takes the fight back to the canvas.
In an attempt to turn the tide, Marquardt opens the third and final round with a takedown attempt of his own but the 10 minute beating he has just taken leave little in the gas tank for him to complete it. Within seconds, he's once again on his back with Sonnen pounding away on him.
There's a moment, with about two minutes remaining in the fight, where a Sonnen takedown again almost leads to another guillotine choke. The Team Quest fighter's face is visibly strained but unlike Silva was able to do six months later, Marquardt cannot finish the submission.
Sonnen never stops attacking, he never relents. And after 15 minutes, he's earned his title shot.
Now can he finally earn the title?