Baki is a jounin level shinobi from the Hidden Sand Village. He's the sensei of Gaara, Kankuro and Temari, and oversaw the three's progress during the chuunin exam. Not much is known about him, except for the fact that he has more up his sleeve then just the chuunin exam. He retreats from the fight with Genma together with Kabuto after the failed invasion on Konoha.
He's also the one who should be held responsible for the death of Gekko Hayate who was eavesdropping on a conversation he and Kabuto were having about their planned invasion of Konoha. Baki wanted to kill Hayate himself as a sign of trust between the Sound and Sand. Although it may not look like it in the beginning, he really cares for Gaara, Kankuro and Temari. He currently seems to be serving on the Hidden Sand's advisory council. He's very loyal to his village.