Shirou Ashiya / Alciel is one of Satan's Demon Generals and was also transported to modern day Japan with him. Extremely loyal to Maou, he takes care of the domestic duties at home and goes to the library to research ways for Maou and himself to regain their powers.
Back in Ente Isla, Alciel was known widely as the right hand of King Satan and a master strategist, making him both a trusted adviser and top military commander to the ruler of the Demon Realm. However, he shared his leader's belief that humans lives are meaningless and expendable, considering demonkind to be superior beings and showing a strong sense of pride bordering on extreme arrogance.
While living in Japan, Ashiya has come to accept his rather mundane life, though he still openly laments how low they have fallen since arriving on Earth, and still tends to consider humans as beneath him. Due to their lack of sufficient funds and personal comforts, Ashiya has become incredibly tightfisted and strict about the household budget. One part of him that has not changed, though, is his extreme dedication and loyalty to the Demon King.
(Source: Hataraku Maou-sama Wikia, edited)