The man who would be Mercenary.
Despite being a "jerk" with a short fuse on his attitude, he is reliable, and often forms a backbone of a combat group when it's needed.
Res-Corp. Model 3-1 9.5x68mm Semi-Auto Sniper Rifle - 4 six-round magazine.
Res-Corp. Custom Model 2559 .459c Magnum w/ 4 12 shot magazines.
Res-Corp. Ka-Bar.
Armoraude Type-5 Light Combat Suit: Torso, Arms, Legs.
Despite being a pilot of a Mobile Suit (XG-139-BRAVO Kintaro on GW.com), he did have S.W.A.T. training before taking it up, giving him formidable experience when entering hostile structures, however, he is most often posted to adjacent roof-tops and set-up to snipe hostile forces that expose themselves and remove them as threats for the rest of the force to take control of the building.
Upon arrival in in the ensuing Conflict (GWC), he planned a feigned capture by one side (White Fang) of the conflict. He gained extreme notoriety due to his merciless nature in combat, and having just a few days before his "capture" having shown up most of White Fang's Mobile Suit pilots during an attack on their capitol ship, Libra, to gauge their estimated strength. Sensing an extreme weakness in most of White Fang's pilots, as well as their potentially wavering loyalties, he found he could have essentially destroyed it from within. After his capture, he set in motion a plan to actually join White Fang's ranks. The plan succeeded, and nearly all of White Fang's pilots jumped ship and joined other factions in the conflict, including White Fang's leader, Gabriel Kushrenada, who founded Black Fang and set in motion a plan to finish off what was left of White Fang, including Duo himself. Though this never happened, as within a few months, Black Fang had dissolved and the members had either ceased fighting, finding it useless to continue fighting, or had gone to yet other factions, that had also gone under, unable to match the tenacity of White Fangs few remaining members.
Eventually, Gabriel would return, without Black Fang, but with a smaller, more loyal group, to keep his plans in motion to finish off White Fang, but never succeeding, with nearly every battle ending in stalemates, or with one side falling back and regrouping and turning the tables on the other. Eventually, Gabriel abandoned his plans, and his loyalists, to never be heard from again, forcing his Remnants to scatter to the wind.
It was a hollow victory for White Fang, one that left him dejected. The worth to his life - fighting, combat, war - had come to an end, and with his rival having disappeared without a trace, he lost the one thing to fight against to prove his was the better warrior. While a fight does bring some joy to him, he does know it just isn't the same without his rival.
In the span of his life, he had gone from mercenary to a vital member of a group he called his family, back to being a mercenary when his family vanished - perhaps lost to assassins, perhaps having gone into hiding. He does not know, as he has not heard from them in a very, very long time. Perhaps, some day, he will see them again, but he doesn't hold out hope for this - as far as he knows, he is the only only still alive from that point in his life.