I was thinking Gandalf might be the most interesting figure of the adviser/mentor types.
His back story is probably even odder than Merlin's. He has strong parallels to Odin without being a jerk. He has one of the great and most oft repeated lines that I will post in full instead:
"`You cannot pass,' he said. The orcs stood still, and a dead silence
fell. `I am a servant of the Secret Fire, wielder of the flame of Anor. You
cannot pass. The dark fire will not avail you, flame of Udûn. Go back to the
Shadow! You cannot pass.' "
or the movie version
"I am a servant of the Secret Fire, wielder of the flame of Anor. The dark fire will not avail you, flame of Ûdun. Go back to the Shadow! YOU! SHALL NOT! PASS!"
He was a loremaster, humble, kickass swordsman, brave, wise and yet remarkable for fireworks and smoke rings.
So he is my suggestion for the best. Though I can well see arguments for Merlin.