Who is Luthe from The Hero and the Crown and what is their importance?

Luthe is a young, blond man who lives in the mysterious north. Luthe is an immortal mage who trained with a master alongside Aerin's mother and her uncle, Agsded. Luthe comes to Aerin in her dreams after she kills Maur and finds herself badly injured. Luthe calls to Aerin to come to him. and eventually she does. When she does, not only does Luthe heal Aerin, but he is able to tell her things about her mother she never would have known otherwise and to teach her enough magic to help her save Damar.