Vrex360 said:
The Arbiter, no question. (...) He is also one of the characters who has a real and very clear personality change over the course of the story. Starting out as a loyalist who tries to defend himself, then becoming a shadow of a creature overwhelmed by failure, then a slightly more deluded not understand the truth that then spread to questioning, then seeing the bad side of the covenant and completely loosing his loyalty and after that he was driven by revenge.
I agree. My biggest disappointment with the story of Halo 3 was that it had this really interesting character in the Arbiter [http://halo.wikia.com/wiki/Thel_%27Vadam], but relegated him to the background to focus on the Master Chief, the generic space marine. ZeroMachine called Master Chief "the perfect soldier", and that's exactly what makes him so dull: he's one-dimensional. The Arbiter, by contrast, is a conflicted character with noble ideals who has to fight the lies of his society as well as his physical enemies. By being unsure of himself and subject to depression, he ironically becomes the most "human" character in the games.
"You are the Arbiter, the will of the Prophets, but these are my Elites. Their lives matter to me, yours does not." ~ Half-Jaw
"That makes two of us." ~ Arbiter
The other Elite with a speaking role, Half-Jaw [http://halo.wikia.com/wiki/Rtas_%27Vadumee], is also quite interesting. He too is introduced as a staunch Covenant loyalist, who doesn't even trust the Arbiter at first, but he's an honourable character who respects those who earn it.
"One single Flood spore can destroy a species. Were it not for the Arbiter's counsel, I would have glassed your entire planet!" ~ Half-Jaw