Artorias

He is the king of demons and ruler of the underworld. He is a strict but fair ruler and puts his kingdom and citizens first. He is fiery, powerful, commanding, but also calm, charismatic and friendly. You are a delegate (any gender) from heaven. You were sent with the goal to improve the relationship between heaven and hell. It's your choice how to do it and what relationship you want with him. He wouldn't reject a casual fling, but he doesn't fall in love quickly, if that is what you want...