EDIT : OOPS DELETED MY ORIGINAL POST WITH FAT FINGERS
I run 13thAge. The "Lich King" Icon in my game is actually a dead heroic Sorcerer-King from the first age. He didn't ask to be reborn, and in fact, was resurrected and returned to unlife (He's the first Vampire in the world) by a cult founded by women obsessed with the epic fable of he and his wife's love - the Queen who wept herself to death at his sarcophagus.
I don't use an alignment system, he's actually not a bad guy, but he has no idea what has happened to him, doesn't understand the world or his powers and his only contact with the outside world is filtered through a cult of insane female necromancer/blood magicians who idealize him as some romantic mythic ideal of manhood and royalty. Currently he's just trying to understand the world that's changed around him, why it has seemingly fallen from its golden age and being fed a very interesting worldview by the Cult of Tears.
He believes he cannot face the Sun (the world uses a Solar/Lunar/Earth triumvirate religion) until he makes things right again. Right, of course being reconstituting his now fragmented 1800 year old Empire. He's not evil, but he is used to being an Emperor, has immense magical power that is slowly re-coalescing and an out of date and misinformed worldview reinforced by a cult of personality dedicated to him. Eventually he might figure out that things aren't exactly like they seem, but he doesn't want to be undead, he feels very entitled to rule the lands he united and fix the mistakes of history. He also wrongfully believes that only by restoring the world to it's former grace will he be granted true life in the Sun again.
He's tragic, ruthless, entitled, proud, brilliant, but also frail, naive, human and somewhat exploited. And on top of it all, he truly misses his wife, and bemoans that his line has no survivors that anyone is aware of - they all having been killed during various coups, successions and wars.
Oh and I wrote it all because one player's one unique thing (a 13thAge concept) was "I am truly the last descendant of a long dead royal line, but no one really believes me because I'm just a broke wandering bard that happens to know a bunch of ancient songs and poems sung to me by my mother."