well...
Some interesting comments everyone
Well, some clarfications... just hope none of my players read this, lol...
this Alhoon has been manipulating the party since around level 4. Him and a VERY old elf (whom is also an outcast) had been playing a insidious game of chess with the party. Seems that after millenia, you get bored... and you have to do things to keep yourself sharp and sane. So these two kindred spirits decided that chess would be how they do it. The elf sends his minions to manipulate the party, ussually in a move against the minions of the alhoon, then the alhoon gets a turn vs. the elf. They have specific game rules they follow and basicly many of the adventures became one move by one or the other. It took nearly a year to unfold this plot mind you. All done very subtlely.
The big twist was when the elf was discovered to be one of the manipulators... and sometimes fate works in strange ways... he fell in love with one of the party members. So after unumerable plot twists he confessed to the entire plot and decided to quit out of the chess game. The alhoon did not take kindly to this and now considers them all their enemy.
The alhoon unfortunately isn't exactly free to do as he wishes. He's a very old figure in illithid history... he is THE first alhoon. He lived in an alternate prime material that the illithids had mostly conqured. They ruled several worlds within. In one of those worlds the Alhoon rose to power, experimenting with genetics, unlife, and foul magics. As he grew in power, his experiments became larger and larger. His power became so much, his experiments involved the entire world he lived in. Over time killing most of the world he lived in, including his own people.
When the other illithids found out about this, they all turned on him. They weren't able to defeat him, but they did imprison him within the planet (100 or so illithids still live there, keeping guard). He cannot escape, but he can astrally project, so he found a sort of freedom in that. He is seeking a way out of his prison, continues his experiments and he has other ambitions (this is a FR campaign, he wishes to pick up where Karsus left off and succeed where Karsus failed, but that's a VERY long term plan).
So that's the situation with this alhoon.