The Half-Demons are known as Carsaeus, and they actually don't need to be the direct spawn between a mortal and demon, simply that whatever bit of demonic essence from their linage has become more notable in that one person. They have the unique properties of being more attuned to the Inferno, which has various bonuses, and of course a few flaws with it. But you get to be half-demon! Ain't that sweet?