I'm gonna say Javik from Mass Effect. He had one of the worst backstories anyone could ever have. Seriously, if you think about it...
[mild spoilers]
to have an ability that won't just leave you with your own memories of living in a broken empire a century behind any feasible attempt of saving it, but the memory of 20 other soldiers who also had to thanks to the beacons, that must leave you messed up. The snippets he tells of are truly horrifying (like how the Reapers appropriated their children so the Protheans wouldn't shoot, or about the death cult on that one planet, just the psychotic strictness of Prothean rules probably necessary to make soldiers fight such an unfathomable evil...). And then, if you let him regain his own memories - well, there's a reason he says he wants to commit suicide after the fight against the Reapers ends if he's seen those, right? Anyway, he's an asshole, but there's really good explanations for it (litereally any person who has ever liked him, known him or even heard about him, even someone who just shares a marginally close cultural context with him is dead and long, long forgotten), but he's not a woobie or "fixable". I always liked that.