Demons

Demons are supernatural creatures that inhabit Hell. Demons were either previously human sinners that died and were sent to Hell or, similar to Charlie's case, native to Hell and are naturally demonic in nature, and thus were not previously human.

Description
Demons come in all shapes and sizes. Their physical forms typically have characteristics associated with the human body, with the exception of having human ears and sometimes lack of a nose.

Some demons can alter parts of themselves, such gaining an extra or new set of appendages such as an extra pair (or more) of eyes, horns, or simply just get enhanced versions of their default form's body parts (such as the rest of Charlie's teeth becoming pointed fangs).

The typical abilities that demons possess are the ability of longevity, different varieties of magic, and even the natural abilities of the entities their characters are based on, such as electricity, night vision, heightened senses, and hunting instincts.

Demons typically don't die easily, but though Sinners cannot be killed by normal weapons and means, all demon types can be killed by the weapons used by Exorcists. Despite Hellborn demons being more mortal than Sinners, there are some Hellborn such as "Demon Royalty" that can only be killed by Exorcist-based weaponry, such as Stolas.

When hit by their weapons, it results in the body of the demon getting "killed off", with the dark energy that's left in the soul to wander into inanimate objects in its surroundings, which explains why some things such as regular furniture have functioning eyes. However, it is unknown if fallen angels, such as Lucifer, would endure the same fate as they are neither Hellborn nor formerly human.

Vitality of a demon is different across species. Demons are able to consume food and the like, suggesting the need the intake in order to survive, which is supported by the Wrath Ring's essential role in food provision. As for age, Sinners stop aging once they are turned into demons and remain the same age as when they have died (ex: Alastor dying in his 30s will remain 30 years old for the rest of eternity in Hell).

As for Hellborn demons, they are proven to age, albeit far slower than humans (as shown in The Magne Family portrait of 1875), maturity and intellect-wise, but they show little to no changes when it comes to their physical forms. It has also been stated by Faustisse that just because they live for a long time, it does not make them immortal, suggesting that they can still die of natural causes.

Culture
While Demon society is very diverse, there are two general groups of Demons in Hell: Sinners and Hellborns.

Sinner demons are humans who have done bad deeds on Earth that resulted in their punishment of being sent to Hell and thus being transformed into demons. Whereas Hellborns are "original" demons that are born in Hell, thus them not having had any experience in the human world or any experience as a human. Unlike the sinner group, Hellborns are broadly applied to all Demon species, regardless of disparate each species is. Additionally, Hellborns are able to traverse across any of the Rings of Hell, whereas sinners are confined to the Pride Ring of hell.

Demons of Hell govern by a hierarchy, and it is dominated by Lucifer Magne above all other demons (even Satan and Beelzebub). This hierarchy is divided into tiers; going top-to-bottom, it is as follows:
 * Lucifer Magne, King of Hell
 * Charlie Magne, heir apparent to Hell's throne
 * The Seven Deadly Sins
 * The Demons of Ars Goetia, which includes Stolas
 * Overlords
 * Regular sinners
 * Succubi, Incubi and other unknown species of demons in Hell
 * Imps and Hellhounds, the bottom of Hell's society

The existence of the tiers demonstrate exceptions to the hierarchy system. The first being that a demon's status is treated variably. For instance, Charlie, despite being the second-highest-ranking demon, is not respected by the populace due to their spiteful climate. Rather, respect is dependent on the power and intimidation of one's character, like in Lucifer's case. Furthermore, demons can elevate their status by accumulating dark powers, which they receive by making deals, soul dealing, or even taking it by force. These beings can rival higher-ranking Hellborn demons and the royalty of Hell, although the royalty is still considered above them. The hierarchy also states that not all Hellborns are inherently above Sinners: different species of Hellborns have a designated standing. For example, Imps are considered the lowest of demons in spite of being Hellborn demons, and the canine-like Hellhounds are demons for hire.

There is, however, a specific type of stronger than average demons referred to as Overlords, which counts as virtual Gods of the underworld. These demons possess enhanced abilities and frighteningly destructive powers that no mere demon can match, granting them a high place in Hell's hierarchy. They usually obtain/enhance their powers by making deals with other demons as well as dominating them in battle and taking in their dark energy.

Demons have their own languages similar to how humans have a wide variety of languages, as revealed when Charlie is said to be fluent in every demon language she has learned while growing up. Although they have yet to show anyone speaking in this language, as of now the characters have only been shown to speak human languages such as English (for the most part) and Spanish (by Vaggie).

The demon civilization is not that different from that of human civilization as they also have laws, facilities such as shops, news stations, bars, etc. and a hierarchy that is to be followed and respected. This also applies for their forms of technology as it is also not that far off from human technology, but with their own twists to it.

Most demons hold little to no value for the preciousness of life. Being part of a society wherein many individuals share the same traits, demons have come to objectify any and all life forms, allies and enemies alike. As such, they tend to treat each other and themselves as disposable commodities.

While there has never been mention of demons practicing any form of spiritualism or religion, the existence of a sign that says "Satan Bless" that can be seen being held by a homeless demon in the pilot episode of "Helluva Boss" coupled with Demons' tendency to swear by Satan's name in lieu of God, implies some sort of belief system or revering attitude at least with Satan. Additionally, VivziePop has mentioned that they also celebrate Christmas but instead of Santa Claus, they eagerly await Krampus' arrival.

Appearance
Demons tend to have an overarching theme to their design. They can resemble animals (some more so than others), objects (such as Vox and some gun-esque demons), homunculi, and more, coming in a wide array of colors, appearances, sizes, and structures based on what creature their character is based on. According to Vivziepop, Hellborn demons appear more monstrous, whereas demons that appear more humanoid-looking, such as Lucifer and Charlie, are actually quite rare.

Demons can have either only one eye (Niffty, Cherri Bomb, etc.), two eyes (Charlie, Alastor, Angel Dust, etc.), or even several eyes (Sir Pentious, Helsa, etc.). A feature consistent to all demons is their lack of human ears in their default forms ; this, however, does not mean ears are completely absent, as humanoid demons such as two of Verosika's crew have pointed ears and animal demons like the Hellhounds and Husk have ears. Aside from their origins, there are physical differences between the two types of demons; Hellborns don't look human at all and have various different species, such as Imps and Hellhounds. This is unlike the Sinners, whose appearances are highly individualized.

As shown in Helluva Boss, humans are able to see and interact with demons despite them being classified as souls.

Abilities
Most, if not all, demons share the following traits:
 * Demon Transformation: Some demons have demonstrated the ability to transform into larger, stronger, and more demonic alternate forms. So far, Charlie, Helsa, Katie, Alastor, Verosika, Stolas and the succubi demons have been capable of this. According to artist Faustisse, all demons can transform when enraged or when in combat.
 * Longevity: Demons, at least for Sinners, do not die of old age and most of the other natural causes that kill humans. However, they can still be killed once they are hit with any of the Exorcists' weapons, or if they have been infected by Hell's own diseases and the like. This trait appears to be exclusive to certain demon types, since Imps are capable of dying and aging naturally, while higher-ranking demons like Charlie have been alive for centuries.
 * Human disguise: As revealed in "Spring Broken", demons are able to shapeshift into their human counterparts in order to infiltrate the living world. Though, it is left unclear if this is only a feat that Hellborns possess or if Sinners also display the same ability.
 * Unique abilities: Demons have a wide range of abilities, the types of which are occasionally attributed to certain Hellborn species, such as the succubi's ability to manipulate hormones. For Sinners, they possess abilities that vary for every individual, depending on their demon form.

Reproduction
As mentioned before by Vivziepop, Sinners cannot reproduce, although Hellborns can. In the case of Charlie, her birth is yet to be explained as Lucifer is the only known Fallen Angel in a relationship with Lilith, a demon whose origins are unclear.

Sinners

 * Angel Dust
 * Vaggie
 * Niffty
 * Husk
 * Sir Pentious
 * Cherri Bomb
 * Katie Killjoy
 * Tom Trench
 * Mimzy
 * Baxter
 * Mrs. Mayberry
 * Arackniss
 * Henroin
 * Lyle Lipton
 * Loopty Goopty

Hellborn Demons

 * Charlie Magne
 * The von Eldritch family
 * Frederick von Eldritch
 * Bethesda von Eldritch
 * Helsa von Eldritch
 * Seviathan von Eldritch
 * Fizzarolli

Demons of Ars Goetia

 * Stolas’ family
 * Stolas
 * Stella
 * Octavia

Hellhounds

 * Loona
 * Vortex

Imps

 * Blitzo’s family
 * Blitzo
 * Tilla
 * Barbie Wire
 * Moxxie
 * Millie’s family
 * Millie
 * Lin
 * Joe
 * Sallie May
 * Wally Wackford
 * Striker

Succubi

 * Dia
 * Verosika Mayday
 * Verosika's crew
 * Josh
 * Kat
 * Milky
 * Kiki
 * Apple
 * Coco
 * Ace

Overlords

 * Alastor
 * Vox
 * Velvet
 * Valentino
 * Rosie

Artificial Demons

 * The Egg Bois
 * Robo Fizz

Wildlife

 * Fat Nuggets
 * Bombproof
 * Queef
 * Vark

Others

 * Lucifer Magne
 * Lilith Magne
 * Crymini
 * Razzle and Dazzle
 * Summer

Trivia

 * If a Demon dies in Hell, the dark energy within them wanders off and possesses random everyday inanimate objects such as furniture and tools, which explains why some of the things seen in the background and such have functioning eyes.
 * So far, male and female Demons exist in terms of Demon culture's gender dynamics. In the case of Hellborn Demons, however, it is unconfirmed if some species possess gender-based names or share a gender-neutral common name. For instance, in Abrahamic religion, a lust-based demon is traditionally known as a succubus for females and an incubus and males, respectively, albeit this distinction has lessened over time. Succubi and incubi exist in Hell, but the male and female lust Demons that have appeared together, such as Verosika's crew, are collectively labelled succubi, seemingly excluding the term "incubus".
 * Shades of gender identity are also hinted at, with Sallie May being the first Demon confirmed to be transgender.
 * Since Demons theoretically can not die via natural causes, such as illnesses and overdosing, they are able to consume amounts that would be lethal to humans without any risk of dying.
 * This is shown in both Angel Dust and Husk as both are able to consume vast amounts of drugs and alcohol without any threat of death.
 * This does not mean, however, that there are no negative side effects, as Loona makes clear that Demons can still get hangovers.