It has got to be Vegeta from Dragon Ball. While he was mostly the same althroughout Dragon Ball Z, his character arc wouldn't start until the Majin Buu saga, and he develops even further through Dragon Ball Super. He started off from being prideful in being the Prince of all Saiyans, even after the destruction of Planet Vegeta, to becoming prideful in defending the Earth, in his family, Bulma, Trunks, and Bulla, and even in training with the only other Saiyan he knows, Kakarot, or what the Earthlings would call him, Goku. Hopefully this will mean Toriyama will finally write an arc where Vegeta is the one having the victory over the main antagonist, rather than Goku taking the W (Resurrection: F, cough).