I have an NPC that I designed for a campaign I'm in... his name is Dariul Lyle.
He cries himself to sleep every night.
He's a Rogue 8 / Assassin 10th, chaotic neutral. For decades he worked as the guild's most successful assassin, over which time he began to see the results, even if indirect, of his actions (he was a genius, after all).
He had always valued personal freedom, but it became clearer and clearer to him that no one who would ask him for a job cared one whit about such a 'romantic' notion. The money was kind of pointless - he could support his wife and children for a century on his savings alone.
His children...
There was no reason for him to continue what he was doing, except for 'guild retribution' - but he had no reason to worry about a group he developed training sessions and techniques for.
Over time his concious began to return, or at least some semblance of one. The damage he has done, once a scratch, became a mortal wound to some very noble organizations. And no matter how hard he tries, he can never set everything right again.
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Not having my original description with me, this isn't a very good personality sample, but you should get the idea - I made it a plot point
