The King of the Kingdom of Llylgamyn at least in the first game. He was in the possession of the all too important amulet the set off the events of the first game... until Werdna stole it from him and created the dungeon the game's set in.
He's insane, Trebor we mean, and he becomes this after years of attempting to thwart the dungeon werdna has orchestrated. He is also your employer in the first game, claiming to reward any soul who returns with the amulet with a place in his personal army and riches.
The man makes good on his promise. at the end of the game, the party is treated to a 50,000 Gold and 50,000 Points of Experience. They, the returning heroes, are marked with a little medal that is proof of their heroics. Of course that mark doesn't mean quite as much seeing as after werdna is slain, he comes back whenever you revisit his chamber. This is helpful for those wishing to grind up characters for the second and third scenarios.
Trebor seems to be rather cunning and a military genius. The proof of his brilliance is his ability to take over the first 4 levels of the dungeon as his own private training grounds for recruits he's scouting to retrive the amulet. Given the sheer asinine horrors found in the dungeon that is quite the feat seeing as he's also holding onto that area of the dungeon. His cunning is obviously shown off with the idea of making adventurers journey through his private training grounds portion of the dungeon! Can't fault him there, players usually find themselves with a decent number of levels by the time they reach the fourth level and with the appropriate caution necessary for traversing the depths below that!