Mathias (spoilers)
I really liked how he was an adversary in the beginning but by the end of S4 he was an ally of Walt's.
But was there anything that caused him to change his attitude about Walt? I know that he disliked Walt because of Walt arresting his former boss. The only thing I can think of is that he slowly saw Walt and his attitude and realized that Malachi was wrong and that he (Malachi) was in fact using his position as tribal chief to run an extortion ring.
But still, was there any one specific event that caused Mathias to trust and basically work with Walt?