The Story of Karthus
Karthus was a mortal who found death beautiful. Most people find this alarming; Karthus found the alarm itself evidence of a failure of imagination. He saw in death not an ending but a transcendence — the moment when the noisy, confused, self-concerned individual self finally dissolved into something larger. He devoted his life to being as close to death as possible, which led him to the Shadow Isles.
On the Shadow Isles, he found what he was looking for: an existence beyond mortality, a community of the undead, and a role he understood perfectly. Karthus became the Deathsinger — a lich whose music is a dirge that literally kills, whose presence is a walking proclamation that death is not to be feared. He wanders from the Isles to bring this message to the living, which the living find significantly less comforting than he intends.
The tragedy — which Karthus would not recognize as such — is that whatever he was before is gone now. He wanted to transcend the individual self, and he succeeded. But the transcendence cost him the capacity to understand what he lost. He is happy, in the way that things without meaningful interiority can be happy. He sings. The song kills. He considers this a gift he's offering. He is, in this, entirely sincere.