Anyway, I wrote up a backstory for my character in this setting, and since I liked the concept I figured I'd stick it on LJ too:
Before the aliens invaded, Gabriel Damon Sullivan was a rather geeky, dumpy, unmarried registered nurse with a good job at a local hospital. He was kind-hearted, deeply religious, painfully shy, and something of a coward. After the hospital where he worked was destroyed in the invasion, Gabriel signed up for an experimental 'super-soldier' process because he wanted to be of more direct help in the war.
The process was successful in some respects. Gabriel emerged transformed: tall, strong, handsome, and able to channel a kind of energy that he could use to heal himself or others, create protective force-fields, and fashion into wings and/or a force-blade, or channel into his own body to make himself supernaturally agile, tough and strong.
Gabriel did not, however, adjust well to his own powers. He did more-or-less all right with healing and making force-fields, but he felt a certain alienation from his own appearance -- he liked the new look well enough, but he didn't look like himself any more, and it's weird. He was also conflicted about his more direct combat-oriented abilities, a problem that worsened in actual combat. Eventually, he experienced a psychotic break and split into two different personalities. The "Gabriel" personality has the healing/forcefield powers, and is pretty similar to his original personality -- devout Christian, nurturing, likes helping people, considerate of others, shy, a virgin who believes in the ideal of traditional marriage, etc. The "Damon" personality has the direct combat powers (tough, strong, agile, can summon a force-sword) and is in many ways the opposite of Gabriel: irreverent, capable of cruelty, flamboyant, flirtatious, actively bisexual, careless of rules, etc. Damon is not evil*: he'll still support a team, and he regards hurting innocents as wrong and wants to fight to stop bad guys and fight off the alien invaders and such like. But Damon's not especially scrupulous about what methods he uses to stop what-he-considers bad guys.
* There is honestly no point in me making up an evil PC. I am lucky if I can make a convincing NPC villain when I'm GMing. I do not like bad guys and am not good at villains. Even if I planned for Damon to be evil, he would end up as "just misunderstood" and never do anything very bad on camera.
The two personalities share the same body, but they don't look the same: Gabriel has a clean-cut, square-jawed look, with short blond hair and blue eyes. Damon has a similar facial structure -- they look like brothers if not twins -- but with an androgynous pretty-boy slant: lean and powerful, with long dark hair and dark eyes. Gabriel has no memory of what Damon does while Damon is in control of their body. Gabriel thinks of Damon as a monster created by the super-soldier process, perhaps even a demon that possesses him, and definitely not a part of him. Damon remembers everything that Gabriel does, and thinks of Gabriel as 'my wimp-ass alterego'. Damon knows he suffers from a psychological disorder, but doesn't care: he assumes any 'treatment' would consist of suppressing his personality in favor of the Gabriel persona. Either personality can handoff to the other voluntarily, in theory: in practice they can't stand each other and won't if they can help it. Shifts also happen involuntarily: Damon tends to seize control if Gabriel is under imminent physical threat. Gabriel tends to seize control if someone is badly hurt and needs healing.
Shortly after their multiple-personality disorder developed, Damon got them kicked out of the military for (a) being insane and (b) violating a slew of rules and a few laws in a mess-hall brawl with some gay-bashers. He was being held in a asylum for the criminally insane (ironically, Gabriel's healing powers are useful for treating some mental illnesses, but not his own, which is one of his arguments for 'I am not crazy, I am possessed'). After the 'helpful' aliens betrayed the Earth during the victory celebration, Damon escaped the asylum in the ensuing chaos.
"Guardian Angel" was Gabriel's original codename from when he first got his powers. Damon uses the same codename himself because doing so annoys Gabriel.
Some side notes about this character:
* I have no idea if I can pull of this concept in a live game, but I love the idea. Enough that maybe I'll try to find an excuse to use it in a story, if the game doesn't last or if I don't like how I end up playing it.
* The concept sets the two personalities in direct conflict with each other: "nonviolent vs violent", "healer vs warrior", "'traditional sexual morality' vs 'if it feels good do it'", etc. There's an obvious and intentional "Gabriel as 'angel'/Damon as 'devil'" parallel, but what I actually want to do is neither promote nor invert that. I don't feel like one of the personas is clearly wrong and the other is clearly right about pretty much any of the things they so strongly disagree about. I don't want to reduce Gabriel to a stereotype of sexual repression or Damon to a vicious killing machine, or anything like that. I want them both to have worthy and legitimate ideals that they find irreconcilable. I do not actually know what the 'happy ending' looks like for this character, but I dislike the idea of it being one persona or the other taking permanent control, or even a simple blending of the two ("some character traits from column A, some from column B ..."). These questions resonate with me because I don't believe they have easy answers
* When I was first thinking of the character, I was planning to play a woman. And then I thought " ... nurturing healing madonna vs violent seductive succubus .... yeeeaah, this feels like well-trodden territory". Changing the PC's gender oddly made the tropes involved more interesting for me. The "virginal nurturing man" is less common than his female counterpart; similarly, mainstream culture doesn't connect male promiscuity with wickedness to nearly the degree that female promiscuity is. And I've seen a lot more bisexual female characters than bisexual male ones. I found that aspect of it interesting; I think most good character ideas will work with either gender, but sometimes they're more interesting as one or the other.