Aleena

Aleena was an asari commando who had a successful career as a mercenary. She was also a friend of Urdnot Wrex, but their friendship was tested when Wrex got a new job. The krogan was hired by a volus diplomat looking to cover his back. The volus told Wrex to kill someone from his past who knew too much... and this person turned out to be Aleena. She and Wrex had a good laugh about it, but there was still the matter of Wrex's contract.

Respecting each other's skills, Wrex and Aleena agreed to battle it out. They chose an old salarian space station overrun with mercs and pirates as their battleground, so no one who got in their way could be classed as an innocent bystander. Wrex pursued Aleena through the space station for days, until he actually ran out of ammunition and had to kill several mercenaries just to get their weapons.

Finally all the others on the station had been killed, and Wrex had Aleena trapped in the medical bay while she patched herself up. But as Wrex began to break in, he realised the station's core had been rigged to overload and just managed to escape before the facility was reduced to vapour. There was no way Aleena could have escaped, but Wrex later got a cheery message from her, saying "Better luck next time..."

Listening to this story, Shepard asks Wrex what he told the volus diplomat, but Wrex claims he told the truth, that Aleena was still alive. However, Wrex saw it as an opportunity, pointing out he was the only one who could protect the volus from her now, and the diplomat hired him as a personal bodyguard on the spot. This lasted until the volus died of natural causes - "easiest job I ever had."