Sadao Maō

Sadao Maō, originally known as Overlord Satan Jacob on Enta Isla, is a demon lord who ends up in Tokyo, Japan on Earth. He tries to make a living while trying to find a way back to Enta Isla. While his role was usually tha of a villain during his time in Ente Isla, he has steadily progressed into heroism since living on Earth. This is shown in such acts like saving people from being killed by an earthquake, protecting the city from either demons or renegade angels, as well as trying to save Chiho and Emi.

Trivia

 * Despite being named after Satan he wasn't always the overlord. In fact, he was at the very bottom of the demonic pecking order, until his life was saved by an angel — Emi's mother, Laylah. While he was recuperating, she tutored him in various things to pass the time, mainly politics, diplomacy and, most importantly, the proper use of military power.