Gunter

A Great Knight of middling class birth, Gunter became a well-known and respected knight in the Nohrian army due to his work ethic and charm. Though he settled down with a family, he eventually returned to the Nohrian army. He was ordered by King Garon to supervise and train his child, Corrin, who was currently residing in the Northern Fortress. Gunter became one of their retainers as well as their main combat instructor.

(Source: Fire Emblem Wiki)