Nothing is really known about Sadao Maou's past. Apart from the fact that he ruled over the land of Ente Isla with four of his war generals, Adramelech , Lucifer , Alsiel and Malacoda . And that he was eventually forced to retreat to Earth due to the inteference of Emilia and the resisting human armies. It is revealed in the light novels that he once was a lowly foot soldier in the Demon armies until he was rescued by Emi Yusa's Angel mother; who preceded to train him in politics and strategy unaware of the consequences of her actions, specifically giving rise to the current demon lord.
Maou, being the Demon Lord of Ente Isla, has shown immense cruelty through his slaughter of many innocent humans, although later on, he does admit that he didn't quite understand what they were at that time. In the human world, Maou is shown to be very caring and responsible, especially to his co-worker Chiho and even to the Hero, Emilia. He is also surprisingly casual and forgiving, as shown when he puts others first before himself. It is possible that this is his true personality, simply brought out by his change in environment.
He appears to be dense about matters regarding women. However, this may be due to the fact that he has only lived on Earth for a short amount of time so far.
His initial appearance was a very tall, dark haired demon lord with a cape to match his position. He seems to have had long, unkempt nails and hair.
Upon his transition to Earth, he lost most of his demonic traits. His eyes are a warm red-orange, and his hair retains its color.
When he had regained magic, he gained a very physically capable body and longer nails instead of his orginal back in Ente Isla. He also has horns on his head, with one that seems to have been broken by Emilia, shown in the beginning of the first episode. In the manga, when he regained his powers in the mall after the earthquake incident, his feet were beastlike and his body is not as muscular therefore not tearing up his shirt. However his appearance during this scene is slightly different in the anime, He is more muscular and has goatlike feet instead.
- On Earth he owns a bike he named "Dullahan" it's name came from the Irish mythology about a headless rider with a black horse and carries his/her head under one arm.
- Satan is primarily understood as an "accuser" or "adversary" in the Hebrew Bible, and is not necessarily the personification of evil that he would become in later Abrahamic.
- Though his character personificates Satan he more likely represents as Baphomet notable with the goat-like feet and horns.