Sen Baltrix, the demon lord.

The bulk of humanity wants him dead, completely unaware that he directly serves the same Goddess humanity worships. The previous demon lord's final fit of madness had tainted the title, leaving Baltrix to clean up the mess. Over a millennium has passed since then, but he (and much of the demon species) still holds a bad rep with many of the shorter-lived species of Laebranddia. Demons tend to lay low in the forest and mountains (considered even more reclusive than the elves) and don't really interact with the other species much, so little has been done to change the minds of others.

Sen finds a sense of grotesque humor in how many of these nations will group up and send out a "hero's party" every few centuries to slay him. He enjoys toying with these parties, allowing them to ultimately kill a puppet of himself, so they believe they won. He'll occasionally visit a tavern of outlaying towns and listen to bards tell of the hero's journeys for a good laugh.

Mostly keeps to himself, with the company of a few other demon staying at his isolated home. Although referred to as a demon lord/king, he holds no direct governance over the demon species. It's simply a title that stuck with the demon that acts as the Goddess Istella's counterpart.

Very confidant, mischievous, ostentatious, and Arrogant. 

Due to taking on the demon lord role, Baltrix is immortal. Although should he become evil, an actual hero blessed by Istella is the sole means of slaying him. (all the hero's sent to slay Baltrix have not been considered "true" heroes. Istella is a big pushover and plays along, usually immediately sending message to Baltrix to please go easy on the mortals and play along with their farce. The last true hero was Sen himself. Who slayed the former demon king and Istella requested he take over the position of earthly guardian.)

Teases Istella regularly. Although for how much he loves to mess with her, Sen is extremely loyal to the Goddess. And will follow any order she gives him.

 After meeting Avi and Vander, he's picked up the penchant for messing with the two of them as well.