"It's simple, really. Cooperate, and you may live to serve us. Resist, and you and your friends WILL die, painfully."
- Wrex, talking to Lucario just before killing Blue Team member Aedran.
Wrex was an immensely powerful Krogan soldier, one of the most renowned of his kind in history. He was the veteran of a thousand conquests, his most notable being the attempt to claim Earth. Though his military was forced to retreat because of the Reapers, his failure was quickly turned to success when the Treaty harvested Sol and nearly obliterated the solar system.
Wrex was very proud warrior, and he is proud of his family lineage of great warriors.
Born Wrex Nukpanka Barbadek, Wrex was born into a family with a history of the males all being successful Warlords of the clan Urdnot. He was raised on the rugged and harsh homeplanet of the krogan, Tuchanka. This rugged world shaped Wrex into the iron-willed, rough-n-tough krogan he is today. As is krogan custom, he served in the military for a minimum of 5 years. However, after his time was up, he decided to pursue his career in the military, because he knew that, as a member of house Barbadek, he was born for war.
Over his life, he forged his reputation in the fires of war on a thousand battlefields. He served in the military for a total of around 200 years. During this time, he led his Urdnot krogan against hostile aliens and other krogan in hundreds of bloody campaigns across the Andromeda. He solidified himself as a fearless, ruthless, and brilliant warrior and tactician. He was praised as one of the finest Barbadek krogan ever produced. He brought honor to his family and his clan, and earned the title Urdnot Warlord-Chief. After his 200 and some odd years of krogan military service, he was recruited by the Andromeda Treaty.
Spectre Saren had heard of Urdnot Wrex's extraordinary accomplishments in the military, and sought to make him a god among soldiers in the Treaty. Saren promoted Wrex to Brigadier, and began sending Wrex, in charge of a brigade of Treaty storm troopers, he was given tasks from the Spectre himself. After a crushing victory against the Batarians on Hurguslad, Wrex was given the rank of General. He was put in charge of a large portion of the Treaty's military. But, he still needed to prove himself further.
After a rebellion broke out on a Treaty planet, Wrex ordered his troops to extinguish it. His troops landed, and were outnumbered by the insurrectionists 10 to 1. However, they still came out in a monumental victory, one that made the battle, and Wrex, go down in Treaty history. Saren then proudly bestowed Wrex the rank of Warlord-General, the highest military rank available in the Treaty. He was put in charge of the entire Treaty military, and hundreds of billions of soldiers all across the galaxy. Wrex was extremely proud of his achievement, and he soon became a member of the Treaty High Council, which consisted of Saren, High Admiral Krebb, and Wrex.
When the need for more energy arose, The High Council agreed to leave the Andromeda and find a new source of star energy. When they found the Milky Way, Wrex was the first to propose a preemptive strike upon all life forms in the galaxy. He knew well; after all his years of experience in war, that new aliens cannot be trusted. Saren and Krebb, however, proposed to seek negotiations first, and if the aliens still resist, then the military could be deployed in full force. When scout ships made planetfall on Earth, they were immediately fired upon by Earthen and Martian ships in combat. They each mistook the ships for hostile aircraft from the opposing faction. They were unaware that these ships came from a completely different galaxy. Wrex, proud of his foresight, ordered the ships to open fire on the aliens. Within minutes, the Treaty ships were already blasting UNSC and Martian Empire ships out from orbit, with more Treaty ships on the way. After barely a year, The UNSC was eradicated, and an extremely large percentage of the human race went extinct. After this point, it became a head-on war between the Reapers and the Treaty, with the crushed surviving humans hiding in the shadows of the warring titans. The fighting continued much like this for a whole century.
Finally, towards the end of the Black Century the Treaty fleets were exhausted by the nearly infinite number of Reapers. The Treaty was forced to retreat from Earth, and The Reapers claimed the planet. However, it was never the Treaty's goal to take over Earth, so they had no shame in retreat. Instead, they returned to their objective, harvesting the parent star, Sol. They harvested its energy on the spot, and caused the star to collapse and supernova, obliterating the surface of all orbiting planets, except the shielded Reaper planet Earth. The Treaty left the darkened Sol system, and took to other human controlled planets in the galaxy, attempting to claim them, and harvesting their stars. After Atmah and Lenor bridged their universes, and the ponies achieved space travel, the Treaty discovered even more sources of star energy in Lenor. Thus, they began mercilessly attacking Equestrian worlds and laying siege to them. Apart from the Reapers, the Equestrians stood as their only resistance.
Ultimately, the Treaty capital world of Palaven was sieged by Reapers and UNSC remnants. Wrex fought outside the Palace of The Spectres, trying to make a last stand against his Reaper enemies. He was eventually attacked by Reaper general Tai Lung, and the two fought for several minutes. Though the veteran warrior Wrex gave the dark servant a deathly thrashing, Tai Lung was finally victorious by indoctrinating the krogan. Wrex died from the attack. Minutes later, Tai Lung died of his wounds inflicted on him by the krogan warlord.
Wrex is arrogant as can be. However, he respects his superiors like a true gentleman. To his enemies, he is a vicious, cruel, and brutal krogan. Wrex hates excuses, and he always wants things done perfectly, exactly when he wants them done. Wrex takes his military career seriously; he does not perceive his doings as duty, but as an act of honor, to respect his ancestors.