Siobhan Wrathburn

Siobhan is a demon - specifically a succubus. Normally, demons are "kill or banish on sight" targets on Federation worlds, but Siobhan is from the only world thus far discovered where the moral polarity of the outer planes is the opposite of where it is elsewhere. On her world, Angels are tyrannical agents of evil and Demons are good-hearted freedom fighters working to aid mortals against repression. After that bit of confusion was cleared up, her world was put under high-security quarantine, but a few members of the demonic legions were allowed to emigrate, for "research" purposes.