There are quite a few characters I could single out from The Wheel of Time series by Robert Jordan. I could probably do an entire year on the main characters alone, but since I think that would not only bore you, but myself as well, I think I'll pass on that idea for now.
I started reading The Wheel of Time series back in my Freshman year of college, which would make it 1994, and didn't finish reading it until last year, 2014. I loved these characters for twenty years, waiting patiently for each new book, rereading them several times in between release dates. When I finally turned the last page of the final book, it felt as if I was leaving behind my family, and that even if I visited them again, it would never be the same. Not only had they changed over a period of twenty years, but my feelings and perspectives on them changed along the way. There are characters I started off loving, and by the end I really didn't care that much about them. There were others, like Perrin Aybara, that I may not have paid all that much attention to in the beginning, but by the end, I was in love with them as much as I was with Rand al'Thor, the main protagonist.
I was going to use a tired cliches and say that Perrin was the one character that changed the most over the years, but none of them stayed the same. Over the period of 14 books, 9,839 pages, and 4,287,886 words, even with a huge cast, it's impossible for the characters to stay stagnant. But of all of them, I think Perrin came into his own the most, and in a funny way, changed the least. I get that he started off as a blacksmith apprentice, and ended up Lord of The Two Rivers, trusted general for the Lord Dragon, husband to a Queen, and King of the Wolves. But who he was as a person; solid, dependable, quiet, thoughtful, methodical, loyal, loving, and the solid bedrock of the group, remained the same. Perrin loves with all his being, he gives himself totally to those who he holds close, and there is nothing he wouldn't do for them. None of those qualities changed, they just grew in scope.
Where Mat was the comic relief of the series, the one who kept everyone from being bogged down in seriousness, Perrin was the heart. He grounds the rest of the characters and keeps them from forgetting themselves and where they came from. I'm not going to go into all the ways he grows into himself, because I really do think everyone should read this series for themselves. If I got too much into his character development, it would ruin some of the journey for those of you who haven't ventured into this world. So needless to say, you are going to have to trust me on this. I will say this, I would die to have his abilities with the wolves, and everything that entails.