Alastor

Sinner Demon
Human (formerly)

Male

30s-40s (biological)

Aromantic, asexual

The Radio Demon (title)
Mr. Radio Demon (by Sir Pentious)
Al (by Charlie Morningstar)
Smiles (by Angel Dust)
Strawberry Pimp (by Angel Dust)
Freaky Face (by Angel Dust)
Mr. Fancy Talk Creepy Voice (by Angel Dust)
Old-timey Prick (by Vox)
Smiling Freak (by Vox)
Boss (by Husk)
Sir (by Niffty)
Sweetie (by Mimzy)
Doll-face (by Mimzy)
Tall, dark and creepy (by Mimzy)
Mister (by Rosie)
King Roach (by Niffty)

Himself
His own fashion style
Smiling
Doodling
Gossip and drama
Invading others' personal space
His mother and her cooking
Jazz music
Strong liquor
Cooking
Seeing people fail
Playing pranks
Bitter tastes
Black coffee
Theater
Dancing
The Stock Market Crash of 1929
Venison
Being in charge
Charlie's potential
Pineapple on pizza
Making jokes

Lucifer Morningstar
"Tacky" circus décor
Susan
Being touched
His hair being touched
Dogs
Frowning
Tea
Anything sweet
Angel's sexual remarks
Being humbled
Post-30s' technology
Anyone ruining his outfit
Being controlled and reminded of it
The idea of the hotel failing
Mimzy bringing destruction to the hotel

Radio broadcasting
Shadow manipulation
Spatial warping
Flexible head
Cooking
Singing and dancing
Bilingualism
Electrokinesis
Video editing
Immortality
Radiowave manipulation
Acoustokinesis
Physical distortion
Demon transformation
Flexibility
Conjuration
Alteration
Demonic magic
Tentacle creation
Umbrakinesis
Shadow warping
Shadow barrier
Pyrokinesis
Photokinesis
Phytokinesis
Fragokinesis
Deal-making
Soul manipulation

Unnamed mother

Charlie Morningstar (business partner)
Niffty (co-worker; daughter figure)
Angel Dust
Sir Pentious (former enemy)
Egg Boiz (former enemies)
Rosie
Mimzy

Vox (rival)
Exorcists
Adam (attempted killer)
Lute

Lucifer Morningstar (rival)
Vaggie (co-worker)
Husk (co-worker; former fellow Overlord)
Unspecified shadow demons (summons)
Fellow Overlords
Rosie
Vox
Valentino
Velvette
Zestial
Carmilla Carmine
Zeezi

Serial killer (formerly)
Radio host
Overlord
Facility manager of the Hazbin Hotel

Alastor stands out from many of the more chaotic residents of hell for his well maintained amiable persona. He gives a first-impression of a good-natured and charming man, wearing a permanently wide grin on his face at all times. His behavior, mannerisms, and even his voice are similar to an old-fashioned radio announcer and speaks with a transatlantic accent, often using quaint anachronisms such as "the picture show" and refers to Charlie as a "charming demon belle". This playful dandyish exterior, however, obscures a much darker side to him - one with high levels of self-importance - and he will not hesitate to use physical violence when others don't act in line with his very particular values or expectations. He is noted to be narcissistic, with his love for himself being stated that no one else can measure up to it, and he does not see many people quite up to his level. Alastor is described as a man of duality. He values good manners, affability and intelligence very highly in others, and will actively look down on those who do not meet his standards, however he will often play fast and loose with these arbitrary rules in regards to himself and his own conduct. Alastor has an odd sense of morality, which is described as "not normal", and has been noted to be quite sadistic, even cannibalistic, devouring lesser demons or those that have incurred his anger. Despite this, he keeps close friends with the other cannibals of Hell, including the denizens at the Cannibal Town. His smiling is a very self enforced form of ego and a show of power and dominance; he looks down on anyone who lets their true emotions show, and even when faced with a rival in strength, if they let slip a frown, Alastor will see them as truly weak. His smile is also to be more unpredictable and unnerving, and gives him a feeling of complete control over himself.

While Alastor is powerful, he is aware that there are other demons and entities that rival him in terms of power, such as other Overlords. For this reason, he is wary around such demons, as they could potentially harm him if he is not careful. Despite everything, Alastor does genuinely seem to want to help Charlie run the Hazbin Hotel, albeit for his own amusement, and hopes for its failure over siding with her idealism. Alastor also dismisses the idea that redemption is possible as laughable, nevertheless, he fulfills his role as patron as promised, providing the hotel with staff, and protecting Charlie and her business from outside threats. He views the whole endeavor as a fun distraction from his decades of boredom. Despite consistently having a confident and cheerful demeanor, he harbors a vulnerable side that becomes apparent when confronted with reminders of being "chained". In this instance, his facade of certainty crumbles, and he succumbs to panic attack. According to Mimzy, when Alastor was alive he would become a "kitten" if he drank enough rye whiskey while jazz music was on.

Alastor is a slim, dapper sinner demon with beige-colored skin, and usually has a broad smile full of sharp, yellow teeth. He is at around the same height as his rival, Vox, with the two standing at approximately 7 feet. He sports a pinkish-red cropped, angled bob-cut with black tips at the ends and two large, black tipped tufts of hair extending from the top of his head, evoking the ears of a deer. The style has an undercut at the back, and two small black antlers protruding from the crown. Alastor's eyes have dark-red sclera, bright-red irises and thin black pupils. His forearms and lower legs fade to dark grey, and he has red hoofed toes and red fingers. Alastor wears a red pinstripe coat with dark-red lapels piped with white, which is ragged along the bottom hem. Underneath this he wears a bright red dress-shirt with a black cross on the chest, and long black dress pants with matching bright red cuffs. He also wears a dark-red oval-shaped monocle, rimmed with black, over his right eye. He accessorizes with a black knotted bowtie with a bright red center, black gloves with red at the fingertips, and black pointed-toe boots with red deer hoofprints emblazoned on the soles. Alastor also carries a thin cane with a sentient vintage style microphone attached to it, which he uses to play sound effects and broadcast his voice.

When in his full demon form, Alastor's body grows larger and limbs become longer, his neck gains extra joints, and his horns grow in size. In one scene in "Dad Beat Dad", Alastor has two sets of horns on his head. His sclera turn black while his pupils turn into the shape of radio dials. His suit and ends of his mouth also gain stitches along them, and the ends of his shoes split to form hoofed toes.