Urdnot Wrex is one of the last of Tuchanka's Battlemasters, rare krogan warriors who combine physical might with biotic power. There is very little of the galaxy he hasn't seen in nearly 700 years of life. Born in the 15th century AD into Clan Urdnot, one of the most respected and influential of all krogan clans, Wrex quickly gained notoriety for his prowess in combat. All krogan males go through a rite-of-passage ritual where they face off against a gigantic thresher maw to prove their worth as warriors.
Most of them can only hope to stay alive against the maw for a specified time before they are deemed worthy of acceptance into the ranks of their clan. Wrex, on the other hand, didn't just stay alive; he actually killed the maw in under five minutes, a feat that hadn't been heard of in centuries, and which wouldn't be equaled for centuries more until Urdnot Grunt accomplished the same feat in 2185.
Having proven himself worthy, Wrex became the leader of a small clan of his own. After the violent galactic war known as the Krogan Rebellions ended with the turians forcibly sterilizing the entire krogan race with the aid of a bio-weapon called the genophage (developed by the salarians), the surviving krogan clan leaders wished to avenge their defeat despite the genophage's devastating effect on their ability to reproduce and replenish their ranks. One of the clan leaders advocating further warfare regardless of the consequences was Wrex's father Jarrod, a warlord who had lived through the entirety of the Krogan Rebellions.
Wrex had a different plan for the future. Realizing that the krogan couldn't possibly win if they tried starting off another war, he led his tribe to focus on breeding for one generation, and slowly inspired other clans to follow his example. In this way, he hoped to slowly rebuild Tuchanka and restore to the krogan the glory that they had lost. Eventually, the other clan leaders started to follow Wrex's lead and set aside their desires for warfare. This angered Jarrod, who decided to invite Wrex to a Crush (a traditional krogan meeting of leaders on neutral ground) with the other tribes. Wrex sensed that it was a trap, but he went nonetheless since krogan tradition dictated that when your father invites you to a Crush, you drop everything and go.
The tribes met at the Hollows, a sacred ground where violence was strictly forbidden. Jarrod tried to force Wrex to acquiesce to his demands, but once he realized Wrex wasn't going to give in to him, he signaled his men to attack. The gathered krogan started massacring each other, and Wrex barely escaped with his life, but not before sinking his blade into Jarrod's chest and killing his father.
The fact that the krogan would engage in violence while standing on the Hollows greatly distressed Wrex, and he realized that the proud race that had once valued courage, strength and honor, now worshiped and glorified mindless violence. Turning his back on the rest of the krogan race, Wrex left Tuchanka and set out to find his fortune in the rest of the galaxy, working as a bounty hunter and gun-for-hire.
The Shadow Broker's Contract
When Cerberus hears that Fist, a small-time criminal who owns the seedy bar called Chora's Den down in the Citadel Wards and doubles as an information source for the Shadow Broker, may be trying to get loose of the Broker's influence, they send Maya Brooks to investigate the possibility of bringing him under their control. At the same time, the Shadow Broker contracts Wrex to travel to the Citadel and execute Fist for his betrayal.
Upon learning of Wrex's involvement, Brooks arranges for several counter-measures to slow Wrex down and prevent him from reaching Fist before she does. First she lies to a group of batarians and tells them that Wrex killed their brother, forcing Wrex to beat them down krogan-style as she heads towards Fist. Then she contracts a group of mercenaries to attack Wrex and stop him in his tracks; this again fails as Wrex grabs a whole bunch of guns and blows up the warehouses that the mercs were in.
While Wrex deals with Brooks' traps, Brooks discovers that Fist has already been claimed by someone else ---- he is now working for the turian Spectre Saren Arterius. Needing time to learn the nature of Fist's deal with Saren, Brooks stages a call to C-Sec and screams for someone to help her before the angry krogan breaks into her home and kills her.
Then she leaves the premises and meets Wrex at the elevator, exchanging a few pleasantries with the oblivious krogan until they reach the ground floor, where Wrex is arrested by C-Sec officers and taken away. It is later revealed that Brooks secretly helped Wrex get free of C-Sec custody, as she liked the krogan's gruff, no-nonsense approach to handling situations.
It is following these events that Wrex meets Commander Shepard at the beginning of the first Mass Effect game.
Powers and Abilities
Wrex possesses the considerable physical prowess common to the krogan, with strength in the 2-3 ton range. He is remarkably sturdy and his stamina seems inexhaustible; in the past, he has pursued targets and fought pitched battles for days on end without rest.
He has spent centuries as one of the most sought-after bounty hunters in the galaxy; consequently, no one wants to cross him for fear of grievous bodily harm coming their way. As a Battlemaster, Wrex is also a skilled biotic capable of terrorizing his opponents with telekinetic blasts and barriers.
The attribute that really sets Wrex apart from the rest of the krogan, however, is his determination for a better future and willingness to lead the krogan to it even if he has to drag them there. When Wrex began to unite the krogan clans, he was hailed as a visionary, and pioneered the development of crop genetics and large-scale medical improvements in place of more armaments. After the genophage was finally cured with the help of Shepard and Mordin Solus in 2186, Wrex's status was elevated to that of a messiah, which he used to rally the krogan armies into battle against the Reapers, proving that the krogan were ready and deserving of the chance to stand with the rest of the galaxy as equals.
Anyone who fights us is either stupid or on Saren's payroll. Killing the latter is business. Killing the former is a favor to the universe.
-Urdnot Wrex, Mass Effect
Wrex is one of Commander Shepard's squadmates in the first Mass Effect game, which was his first appearance in any form of media. Contracted by the Shadow Broker to kill a traitor named Fist who ran the seedy bar Chora's Den, Wrex was pulled in for questioning by wary C-Sec officers when he arrived at the Citadel. Shepard was pursuing Fist for information on the whereabouts of Tali'Zorah, a quarian who claimed to have irrefutable evidence that Saren Arterius had masterminded the geth attack on Eden Prime.
Wrex teamed up with Shepard's squad to track down Fist, and killed the criminal after he coughed up Tali's location. After Tali is rescued from Saren Arterius' assassins, Shepard presents her proof to the council, who then send the commander on a mission to apprehend Saren and bring him to justice for his crimes. Wrex decides to tag along with Shepard, along with fellow aliens Garrus Vakarian, Tali and an asari archaeologist named Liara T'Soni that they free from a dig site under attack by Saren's geth soldiers.
While on-board the Normandy SR-1, Wrex shares his history with Shepard, telling the commander everything about his life before he became a mercenary, as well as after. He grows to trust Shepard, and even goes so far as to say he's never had a more trusted ally after Shepard helps him retrieve a lost set of armor that once belonged to Wrex's forefathers.
That trust is tested, however, when they land on the planet Virmire and learn that Saren has somehow managed to cure the genophage on his own, and has created an army of krogan to serve him in the process. Upon learning of the existence of a cure, Wrex gets angry about being asked to destroy Saren's facility and the cure inside, seeing it as the last hope to save the krogan race.
There are multiple possible outcomes to this situation. Shepard can plead with Wrex to see that Saren is only trying to manipulate the krogan, and that no good will come out of his cure. If Wrex decides to set aside his concerns and trust his commander, they proceed to destroy the Virmire facility together. If not, a conflict will arise that tragically ends in Wrex's death at the hands of either Shepard or Ashley Williams. Regardless of the outcome, Saren's Virmire facility and his genophage cure are destroyed.
If Wrex survives, he then accompanies Shepard on the mission to find the Prothean Conduit on Ilos, and fights in the Battle of the Citadel to stop the Reaper called Sovereign.
Mass Effect 2
Speak when spoken to, Uvenk. I'll drag your clan to glory whether it likes it or not.
- Urdnot Wrex, Mass Effect 2
If Wrex survived the events of the first game, it is revealed that he went back to Tuchanka, determined to stick it out this time and bring about real, lasting change to krogan society. He managed to assume control of Clan Urdnot and then forged alliances with the other clans, forming a strong, consolidated krogan territory. Rather than waste time building more weapons of war, Wrex directed his government's scientists to focus their attention on medical improvements, intelligent crops, and other more practical necessities for a race that was slowly starting to build itself back together.
He even earned the trust of the normally wary female clans, and they approached him with a plan for all clans to have degrees of access to fertile females so as to maximize the chances of healthy krogan births. Wrex knows that swapping krogan females around is not an ideal scenario, but acknowledges it as just one of many compromises the krogan have had to make in order to survive in the shadow of the genophage.
When Shepard arrives on Tuchanka, Wrex warmly greets his old friend and tells the commander about all his plans for Tuchanka. When Shepard asks how the plans are working out, Wrex replies "Better than I'd feared, worse than I'd hoped.". Wrex also assists Shepard in locating Mordin Solus' lost assistant Maelon Heplorn, as well as inviting Grunt into Clan Urdnot once he finishes the traditional krogan Rite of Passage. Shepard asks Wrex to join him on the Normandy to do battle against the Collectors, but Wrex reluctantly declines and wishes his friend well, telling him that he has to stay back on Tuchanka to keep the more unruly clans in line.