Igareth Ijeiska

He was a relative of the Hero Jerga and the seventh in line to the Azesion throne two thousand years ago.

During the Great War, Igareth was captured by the Demon King Army while being escorted somewhere and treated rather poorly. When the Demon King Anos found out, he brought the boy to Delsgade and eventually returned him to a unit of the Demon King Subjugation Battalion in Dilhade. However, a Dragon attacked them while crossing the border, and Igareth became stranded in the demon country. He hid his identity and returned to Delsgade, but Anos had already sacrificed his life by then.

[Spoiler] Igareth has reincarnated four times since then, with his current life being Alamith Eltimo, a third-year student from the Demon King Academy. He didn't remember his past until he was captured by Avos Dilhevia. [/Spoiler]

(Source: Maou Gakuin Wiki)