Hey folks! I need to flesh out an important NPC/Villain for my FR campaign and I thought I'd tap into the creative potential that seems to be abundant around here 
I little backstory:
The party had previously been given a mysterious artifact in the form of a mummified hand by a morally flexible NPC who wanted to use the party as guinea pigs to test its exact function and risks. The artifact was said to increase martial prowess in some way.
The party could not find out anything about the item, so they let it rest for a time.
During a later story arc, the party was being stalked by assassins. One of the party members (an NPC at the time), a physically weak female priest of Mystra in charge of keeping the artifact, was cornered by an enemy who seemed to be immune to magic. There were no witnesses to the battle, but the priest later emerged unscathed, the assassin beaten to death and the artifact nowhere to be found (the priest apparently activated it somehow under duress).
A spirit entity has token control of the character, giving her great monk-like combat abilities. The spirit has communicated that it wants to be returned to its burial site. It radiates strong evil when in control and has already killed several allies of the party who it considered to be obstacles to its plan.
The spirit doesn't communicate directly but will soon provide some clues as to its origins. I want the party to unravel these clues, seek out the spirit's resting place and thus free their companion.
What I need now is some inspiration as to who exactly this spirit was. I need it to be a monk -like figure with legendary martial and strategic skills (somewhat like Sun Tzu), but also with a strong evil philosophy. His identity is supposed to be obscure, but he left behind influential writings that can help piece together his whereabouts.
Sorry, this post became longer than intended...

I little backstory:
The party had previously been given a mysterious artifact in the form of a mummified hand by a morally flexible NPC who wanted to use the party as guinea pigs to test its exact function and risks. The artifact was said to increase martial prowess in some way.
The party could not find out anything about the item, so they let it rest for a time.
During a later story arc, the party was being stalked by assassins. One of the party members (an NPC at the time), a physically weak female priest of Mystra in charge of keeping the artifact, was cornered by an enemy who seemed to be immune to magic. There were no witnesses to the battle, but the priest later emerged unscathed, the assassin beaten to death and the artifact nowhere to be found (the priest apparently activated it somehow under duress).
A spirit entity has token control of the character, giving her great monk-like combat abilities. The spirit has communicated that it wants to be returned to its burial site. It radiates strong evil when in control and has already killed several allies of the party who it considered to be obstacles to its plan.
The spirit doesn't communicate directly but will soon provide some clues as to its origins. I want the party to unravel these clues, seek out the spirit's resting place and thus free their companion.
What I need now is some inspiration as to who exactly this spirit was. I need it to be a monk -like figure with legendary martial and strategic skills (somewhat like Sun Tzu), but also with a strong evil philosophy. His identity is supposed to be obscure, but he left behind influential writings that can help piece together his whereabouts.
Sorry, this post became longer than intended...