Need suggestions for turning a Druid PC into a recurring villain

[Random Poking]

So, one of my players might get his Druid killed soon and then I thought "why not make the Druid a recurring villain?". To justify the turn to evil I decided that the Druid would be corrupted by an evil force. I am a little unsure of which evil force should corrupt the Druid. Demons and Devils are obvious candidates, Fey is also a good choice since I'm running Kingmaker.

The problem is that I don't know what flavor of corrupted I should go with and I need a reason for why I can have the Druid return from apparent death. The Druid also needs a motivation like "You betrayed me, and for that I will destroy all that you hold dear." or "Your kingdom will ruin the land. I will tear it all down and let the nature takes it's rightful place." to match the change.

Any suggestion for how I should do this?

[wraithstrike]

Do you know how the druid will die, and what forces are your PC's rallying against? What is the druid's nature. Some characters can not believably be turned evil, depending on how the group views them.

[Thehthuhthinag]

Body gets raised, but, that 1% chance happened and something else came back instead! The PC whent on to the great whatever and a walk-in inhabited the body. Perhaps a fey spirit, or a recently dead whomever...

Now its the same body but its a different person. Accessing the stored memories of the body so it is essentially the same character, but somehow scewed a little differently. Perhaps Evil, or Neutral.

There are the Uskwood Druids who worship Zon-Kuthon the Evil God, but then there is Evil Green Faith Druids as well. They have vermin familliars and are the winter aspects of nature. They are the Death Cycle of life. Berth, growth, reproduce, Death... They take Decay or Ice as a Druids domain :) They could be Neutral or Evil. And they can hate whats happening in the forrest with human intrusion.

Then there is the Fey Druid, the Neutral or Chaotic Neutral that can follow the fey folk and hate whats going on in the forrest...

[Random Poking]

The Druid is currently outlawed by the other PCs, so the druid will most likely die by their hands. The PCs will try talking with each other first, but it's likely they will remain enemies.

The forces threatening the PCs is the Fey, who are manipulation various factions against them.

The Druid's nature is mostly Player Character. The patron deity is Erastil, but doesn't really factor much into how the player roleplays the druid.

[Oliver McShade]

The Orb of Darkness.

The druid is re-animated as one of the undead. He now has the burning hatred of all living things, but most of all, his former party members who is was closed to.

That consent reminder of joy, happiness, friendship, that he once had, is now a open wound apon his soul. A remember of a life denied him. That fills him with Hatred, revenge, and a burning desire to end his parties members lives.

.......

Alignment: Neutral Evil