Stolas is an anthropomorphic owl demon. He is tall and slender, with a white, heart-shaped facial disk and small black beak, resembling that of an owl. He has two pairs of almond-shaped red eyes, one set atop the other, with no visible irises or pupils, albeit white highlights do occasionally appear when he is excited.

Stolas has gray-blue feathers, which gradients to dark gray-blue on his head and long, plume-like tail. He has a lighter gray-blue puff of fur on his chest. He also has a gray streak on his hair.

His limbs are long, thin, and black, and his feet are tipped with bird-like claws

Stolas gives the immediate impression of someone regal and ostentatious, as would be expected for a royal of his station. He dresses in clothing befitting his role, and his mansion is decadent, containing many large, elaborately framed portraits of himself and his small family.

Underneath these dignified trappings, however, Stolas is shown to be a flamboyant, dramatic, eccentric, and often giddy person. Someone who does not take his royal reputation as seriously as the people around him expect him to, and is prone to act quickly on his easily excitable emotions.

He is also shown to be very intelligent, even as a child, due to being a bibliophile and having incredible knowledge of many things including the laws of Hell.

Stolas can also often get caught up in pursuing his own present interests and fails to pay attention to the more pressing issues around him, including the feelings and needs of others. He has even dismissed their wishes under the belief that, as long as he was happy, everybody else was as well, even when he was told otherwise. He also has trouble expressing his emotions when facing bigger dilemmas such as having a hard time explaining to Octavia that his marriage was never good or standing up to Stella before his affair and having trouble talking to Blitzo about his true feelings toward him. Stolas can be prone to tears when he is under a lot of emotional distress.

Although, these tendencies can make him appear selfish and even airheaded to some people in his life, he isn't oblivious to correction or regret and this is something he makes an effort to improve on, specifically in regards to his beloved daughter, Octavia.

Stolas is also shown to be very lonely, seemingly isolated and cloistered in his position. In "The Circus", when he was a child, he told a young Blitzo that he never had anybody to share his books with, further supporting this notion. Although, he is married, it is clear that he and his wife are not on affectionate terms, and that their marriage is implied to have been somewhat cold for a long while.

Stolas has, perhaps surprisingly, an equally romantic and explicit side, something he looks to indulge in with Blitzo, an imp, considered 'lower-class' among his peers, whom he is currently engaged in a complicated extramarital affair with. He is also very uncensored in discussing his many bedroom preferences, using highly explicit and flowery language, sometimes in front of others, and is interested in aspects of BDSM, such as bondage.

Stolas is invested in Hell's soap operas as comfort shows, enjoys the process of getting ready for rendezvous, and swoons over idealized ideas of amorous romance.