Gaara

General Info
Gaara of the Sand was originally introduced as the third-main antagonist of the Chunin Exams Arc, with Kabuto Yakushi being the second and Orochimaru being the first. After being defeated by Naruto Uzumaki, he became one of the main protagonists of the series. He is now the Kazekage, the leader of the Hidden Sand Village. He was also the jinchuriki of Shukakau, the one-tailed tanuki, but it was captured and stolen by Akatsuki.

Peronality
Gaara was originally kind and always tried to help others. Then he realised that nobody loved him because he had Shukaku inside him. From then on, he only loves himself and kills people for the fun of it. This was until he was beaten by Naruto and Gamabunta, using the will of fire to protect those important to them. To Naruto it was Sakura Haruno, who was captured by Gaara's sand, and Sasuke Uchiha, who was too tired to continue fighting, whilst to Gamabunta it was Gamakichi. This caused Gaara to realise that strength came from protecting those important to him.