Raven is one of the Three Sages of the West and a friend of Shion's. He is also the Head Master at the Ecnovious School of Rituals. He lived in Fool's Town as a child and used to follow Shion around and ask him stuff.
Raven is a powerful mage despite his age. His magic is called "Hell Lesson" and is based on school subjects (Math, Chemistry, Art, P.E...). Each subject is divided into one-hour sessions and each one lets Raven use different skills and abilities.
(Source: Magico Wiki)