Ramsas

Ramsas is the uncle of Mio Naruse. He is also the leader of the Anti-Leohart Faction.

Ramsas looks like and elderly man. He has long red hair, two horns which is one of the usual demon traits. He wears black armor with shoulder armor, as well as long red cape with yellow ornaments.

(Source: Shinmai Maou no Testament Wikia)