In my head, I have created my own lore for how Death Knights should be. Other DK players have told me I’m wrong, but I’m not worried — this is how I like to play my Death Knights.
The following stuff is made up…
Death Knights were heroes who fell and were then made into tools of evil. After the Battle of Light’s Hope Chapel, their old heroic personalities were able to try and struggle back to the surface, but that is only the start of their problems.
In my world, the universe has imbued all things with a purpose and that purpose is tied directly to the thing’s essence. When a thing fights against its purpose, it is attacking its own essence and tears itself apart. Things following their purpose have an easy time, just as water will always take the path of least resistance.
Though they were once heroic, Death Knights were re-purposed by the Lich King and their essence is now evil. It is in their nature to do terrible and wicked things — but in their hearts they are still heroes.
For me, this means the Death Knight will try to do good things but the outcome will always be bad. No good deed goes unpunished. The more they try to bring purity, the more their actions inadvertently spread corruption.
It is as if they are swimming against the current of a powerful river while every voice in them whispers, “Go with the flow. Stop fighting. Let me carry you to where you need to be.”
The Death Knight rebels against the will of the universe and against his own essence and nature and is punished for his impudence. It is the Death Knight’s fate, or doom, to bring sorrow and pain and the fact that he wants to bring peace and joy is what makes him a tragic figure.