Okumura Rin♂

He is the son of Satan, born from a human woman and is the inheritor of Satan's powers. His powers were sealed at birth into the demon-slaying blade Kurikara by Mephisto Pheles, the True Cross Academy principal, allowed him to live a normal human life for nearly 15 years with his twin brother Yukio and his foster father Shiro Fujimoto. Rin becomes aware of his true identity after Kurikara can no longer seal his powers, setting off a chain of events that lead to the death of Shiro at the hands of Satan, who attempts to drag Rin back to the demon realm, Gehenna. Mephisto later confronts Rin, who demands that Mephisto to let him join the exorcists to fight against the demons, who then enrolls Rin into the True Cross Academy so that Rin can pursue his goal to obtain the title of "Meister" in Knight, then become a Paladin and defeat Satan.

Rin has a protective and supportive personality. He can be very violent and tends to get into fights (which are usually caused by strong emotions) but is actually kindhearted. He supports his friends and tries to encourage and help them. He also seems very protective of Yukio, and aims to surpass him one day. Unlike his younger brother, Rin is immature, which leads other people into believing that he is the younger twin out of Yukio and himself. He is headstrong (figuratively as well as literally) and is often very open with his friends. He is also a good cook.

[From Wikipedia & Ao no Exorcist Wikia]