Hazbin Hotel Staff
Alastor assists Charlie with her endeavors; it is currently unclear what their relationship is. However, they have a similar sense of humor.
According to Vivziepop in one of her streams, Alastor thinks Charlie is funny and likes talking to her.
When asked to give his unfiltered opinion of Charlie, Alastor responds by saying he personally likes her smile and positive attitude. In his reprise, he tells her that he thinks she's 'one of a kind' as well as a 'charming demon belle.'
Vaggie is well aware of Alastor's reputation.
Upon Charlie first warning her that the "Radio Demon" was at the door, she insisted she shouldn't let him in.
After Alastor lets himself in anyways, Vaggie is determined not to let him hurt anyone with affiliations to the Hotel and threatens him at spear-point, referring to him as a "pompous, cheesy, talk-show shitlord".
She is distrustful of Alastor's intentions and exacerbated as Alastor continuously infuriates her with patronizing remarks and gestures for fun.
As shown in the pilot, Alastor and Niffty are acquainted with each other. When asked if Alastor and Niffty knew each other before the hotel and what relationship they have, Vivziepop stated that she can't really get into it.
Alastor and Husk are acquaintances. They have worked with each other in the past, as shown in Alastor's backstory and Husk's dialogue. Little is known about what they did together.
In the pilot, however, Husk reacts with animosity upon realizing Alastor summoned him for one of his endeavors, indicating he doesn't like getting pulled into his schemes.
Despite Alastor's power and reputation, Husk doesn't seem to be afraid of him.
The Magne Family
Alastor has yet to interact with Lucifer, at the least on-screen.
During the pilot, he looks at a royal family portrait hung in the Happy Hotel, seemingly recognizing Lucifer.
When asked what would happen if they met, Vivziepop stated that Alastor would kind of like Lucifer; more specifically, Alastor would like Willy Wonka because he's a jerk and since Lucifer has a lot in common with Willy.
Vivziepop and Dave also stated that Alastor in no way would be afraid of Lucifer; there is mutual respect going on between them.
Angel is very much unaware of Alastor's reputation. While taken aback a bit by Angel's offer for a blowjob, he swiftly turns him down.
Sir Pentious claims to have had a battle with Alastor prior to the events of the pilot. However, Alastor claims to not remember any of it.
He brutalizes Pentious after he interrupts his reprise.
Alastor is affiliated with Rosie, though they have yet to interact in the show.
On Twitter, Vivziepop stated that Alastor and Rosie's relationship is very similar to Jack and Mary's relationship in Mary Poppins Returns.
Mimzy was originally written to be Alastor's admirer and later love interest during the production of the show, though this idea was later scrapped. It is unknown what their relationship currently is.