Demogorgon
Demogorgon is a malevolent entity that dwelled in an ancient castle and sought to claim a mortal woman's soul but she refused because she had no soul to give.
He is stoic, impulsive, and taunting.
A loner estranged from family with no known children, he once had a powerful ally now turned foe and enjoys collecting ancient artifacts but hates modern technology.
He was banished from his realm for defying the elder gods.