Who is Ogion from Tehanu: The Last Book of Earthsea and what is their importance?

The Mage of Gont, Ogion, lives in isolatation on the top of a mountain known as the Overfell. Ogion was once Ged and Tenar's teacher, but neither of them stayed with him for long. In this novel, Ogion is old and is dying. Tenar comes to stay with him in his final moments, and it is to Tenar that Ogion reveals his true name..... a great honor that establishes Tenar's position in the eyes of the Mage of Gont.