Urdnot Wrex
Wrex is among the last of the krogan Battle Masters. They are rare individuals who can combine biotic abilities with advanced weaponry. Wrex quickly gained fame for his battle prowess and became a leader of one of the smaller Urdnot tribes at a very young age. To date, Wrex is the youngest krogan to be granted the honor in 1000 years.
Following the krogan genophage (a genetic mutation that causes stillbirth in 99.9% of the krogan population), Wrex realized that his people had degenerated from the honor-bound people they once were and had become senselessly violent, preferring death in battle rather than saving their culture through peaceful means. Wrex turned his back on his people when his father, a krogan warlord who wanted to resume the war, betrayed and attempted to kill him. Wrex escaped, though not before taking his father's life in retaliation. During the past three centuries, Wrex has worked as a bodyguard, mercenary, soldier and a bounty hunter. One operation as a mercenary was with Saren Arterius as his employer, though Wrex had a bad feeling about Saren at that point, and left the contract the moment he met the turian.
Despite his menacing appearance, Wrex rarely loses his temper. Likewise, Wrex doesn't voice his thoughts very often. But when he does, people are more than willing to listen. The mere threat of his anger is enough to ensure that.
Late in the game, at the planet Virmire, Wrex learns that Saren is developing a cure for the krogan genophage to create an army of krogan soldiers. Uncertain as to who he should listen to now, Wrex has an angry confrontation with Shepard over whether or not the facility should be destroyed. Depending on the player's choices, Wrex may survive, or he can be killed by either Shepard or Ashley.