Gaara

Gaara is an antagonist turned supporting character in Naruto making his debut as the central antagonist of the Chunin Exams/Konoha crush arc. He is a sand village shinobi who spent his childhood mistreated for being the jinchuriki containing Shukaku and due to being mistreated and Shukaku's influence Gaara evantually came to the conclusion that his only purpose in life is to kill others however after his fight with Naruto he learned the error of his ways and turned good for the rest of the series.