One of the biggest moments in the first game that really cemented just how much of an impact Mass Effect was going to make on gaming history was choosing whether or not to down Wrex on Virmire. To this day it's a decision that splits gamers right down the middle, and as his subsequent appearances in the trilogy were then governed in either way by this potential outcome, in ME2 he appeared as a Warchief and in 3 as a final battle war asset. In terms of recruiting a big lumbering bruiser it doesn't get much better than Wrex. His reliability and devastating abilities in battle were what led so many people to sparing him in the aforementioned decision, and when it came time to 'replace' him with ME2's Grunt (himself a great character) Wrex ended up feeling a bit underused. As one of the Krogan's fiercest warriors and one steeped in the knowledge of his people, he's a fantastically diverse ally whose allegiances could be tested far further if he's encountered in a prequel-state of the universe, back when he was a bounty hunter. The applications as your team mate write themselves thanks to his skill-set, and if Bioware push the boat out when it comes to race-relations throughout the galaxy, his position as a sufferer from the Genophage in the face of defending his people could lead to some intense altercations.