Byron White

He is a Harry Potter fanon character (therefore created by fans) protagonist of a fanfiction saga The Most Faithful.
He is a former agent of the English Ministry of Magic who worked as a spy for Dumbledore. He attended Hogwarts in the same years as Lily Evans and Severus Snape, with whom he became best friends.

He's been Locked away in Nurmengard for years, now he has a chance to help Dumbledore and the Boy Who Lived.
His name is Byron White.