Marcus Lyons is a 26 year old armsman. Technically, he's a spy for Terra Firma, stationed on Omega to see who among its residents had the money to waste on relic weapons and the inclination to do so. He is normally calm and practical but he can be goaded into senseless personal competitions with no incentive other than the rush of an intense match. He has no professional history outside his weapon shop, but he spent 10 years training his biotic powers at BSI.
Born in 2160 on one of the Sol system's stations, Marcus's formative years were actually spent in relative happiness, complete with a reasonably functional family. That lasted until he reached age 5 and was thus old enough to go to school. At that time, both he and his parents learned the hard way just how much other people hated the 'evil blue lights' that would sometimes flicker around within his body. After a couple weeks of him coming home beaten by other students until he could barely walk, and with no response to their complaints to the school's administration, his parents moved and took him to another school.
More of the same would continue for the next couple years, with his parents moving first around, then to other colonies as they enrolled him into ever more exclusive schools, hoping the relative lack of other students would result in better treatment for him. They were wrong, and he began to develop the mentality that his 'sparks' were defects and that there was no place for him in the world. With that thought in mind, he deliberately avoided boarding the morning school shuttle and went back home. He surprised his mother who was about to shoot herself because she could neither cope with his suffering, nor find a humane solution for it. Paralyzed by shock and still sore from his routine abuses, he could do nothing to stop her.
It seemed, however, that the knack for picking the absolutely most incorrect solution to an emotional crisis ran in the family. The following year, he ran away from home, leaving his father a note stating more or less Marcus's intent to not inflict the pain and misery on his father that he had his mother. It took him all of two weeks to find himself captured by batarian slavers.
For all their merciless indistinction between human children and beasts of labor, the Batarian slavers who removed Marcus from the streets were much more practical about dealing with biotic potential. From his masters, he learned the fundamentals of properly using his abilities. It was more of a massive gambit on their part than an intensive investment, given that even with all the time and money it costs to train a biotic, there was not much of a chance of his powers even proving useful. Especially since he was a human.
However, he turned out to be a rather effective miniature smart bomb. Having become a very weak but reusable explosive that could think intuitively, memorize orders, climb, jump, and squeeze through holes smaller than his body, Marcus turned into a huge payoff for the Batarians. He worked that way for a few years, quietly and obediently finding and destroying smallish obstacles that were in locations to inconvenient to maneuver a machine into.
Incidentally, it was here that he'd first developed his phobia of contact with Asari. A Maiden named Rochillia D'Nace had deliberately gotten herself 'employed' by a slaver ring she knew was using human labor, in order to study the nature of the new species in adversity. If any of her 'research subjects' had heard of Jane Goodall, they would likely have been much more offended than they already were for the simple fact of an alien hanging around their grottoes.
Upon learning that the biotics were isolated from the other slaves by the slaves themselves rather than the batarians, Rochillia had taken it upon herself to try a more 'hands on' approach to researching them in order to find out why. Any one of them would probably have had similar results on her end, Marcus just happened to be the nearest available who didn't reflexively evade her grasp when she came to this decision. The result of this meld turned out to be highly traumatizing for both of them, with her suffering his painful memories and him being overwhelmed by the first meld he'd ever had. They were both reduced to screaming, crying, quivering wrecks in moments.
After he'd recovered well enough to continue working, Marcus made sure to remain out of arm's reach of her and anyone looking somewhat like her for the rest of his life. Once Rochillia got the hint and stopped trying to press conversation, he more or less settled into his life, such as it was. At the onset of puberty, however, he was 'rescued' by Terra Firma soldiers and his world was turned upside down yet again.
Blue Sky Institute
"Enter these walls as outcasts and monsters. Leave them as humans." -Engraved on the opening gate of Blue Sky Institute, a school founded by Terra Firma as an imitation of BAaT. Unlike its predecessor, BSI was not quite as (physically) abusive of its, and being largely populated by retrieved orphans, slaves, and child soldiers, most of its students had a higher resiliencey and lower self-esteem to start with. There were few among them for whom enrollment was not a step up from their past lives, and none for whom it was a step down.