Belarco

Belarco, born Blakal Roselia, is the amnesiac first prince of the Roselia Kingdom and a major supporting character in the Yuusha ga Shiinda! series. Introduced as an adventurer, he is famous for having buried more than 100 devils in a battle three years ago. Belarco appears in all of Touka and his friends' adventures, but the extent of his abilities is shrouded in mystery. At the end of the series, he becomes King of the world.

(Source: Yuusha ga Shinda! Wikia)