He is the Sword Emperor who reigns over Agatha, the land of knights, as well as the "Prophet" of the Selected Eight.

Diedrich is a rather carefree man who has a smile on his face most of the time and pleasantly enjoys the Anos Fan Union's songs. However, he can be serious when needed, as shown during his fight with Anos. Even though there are futures that can't be changed no matter what, Diedrich will still challenge them, as there's no point in prophecies otherwise. He possesses an immense amount of magic power that is nearly comparable to the gods , and a great degree of physical strength

(Source: Maou Gakuin Wiki)