Tanas

Duke Tanas is also known as Oliver and is mainly in Path of Radiance. He is mainly known as a 'protector' of anything beautiful (namely the herons).

Path of Radiance
Duke Tanas was mentioned when it is discovered Reyson was sold to him by Naesala. He is a boss in Chapter 17 area 4. He is also a bishop.

Radiant Dawn
He was supposedly banished from his estate, although he is still there, something Ike and the others learn after being attacked by him and his men. He is recruitable in this chapter (Part 4, Chapter 4), if you get him to talk to Rafiel (which is insanely easy once you clear out most of his men). He will come with a strong light tome (Nosferatu) and a silence staff. He is a saint.