Demons

Demons are a loosely defined race of beings in Dota 2 lore. They inhabit the Seven Hells and a number of subterranean realms, such as the Abysm or Foulfell. Most demons speak the language of Ozkavosh. They are ruled by the Demon Lords. Demon outlaws are imprisoned in the hidden dimension of Foulfell.

Personality
Demons are very egotistical, selfish, and self-centered. They lack a conscience and are more than willing to betray others or their own kind to satisfy their needs.

According to the likes of Void Spirit and Dawnbreaker, demons are creatures of great power and limited intelligence.

Demon Lords

 * : Lucifer (or Lucifash in Ozkavosh) reigns over the Seven Hells as one of the three sovereign demons with the ability to traverse to the material plane unhindered. Despite this ability, he is hardly concerned with the affairs of the so-called "Noninfernals" and "Lesser Spectral Consorts". He seems to have some form of control over the likes of Shadow Fiend and Shadow Demon indicating that he is the supreme Demon Lord among the three.
 * : Among the three known Demon Lords, Shadow Fiend exploits his ability to planeshift into the material plane to harvest souls where they will fall into the Abysm. He is under the heel of Doom and Shadow Demon, indicating that he is the lowest among the three sovereign demons. Besides being a sovereign demon, he is also one of the three current lords of the Court of Ristul.
 * : The very embodiment of the dangers of demonic evocation, Shadow Demon is unique among the sovereign demons in a way that he does not travel to the material plane at his own accord. Instead, he allows himself to be summoned into the material plane by anyone who dares to invoke his presence, before destroying the mind of the summoner and replacing it with his own essence that allows him to control the mindless cultist. In terms of hierarchy, he seems to be in the middle due to being under Doom and having Shadow Fiend under his authority.

Other demons

 * : Also known as Akasha, this succubus of torment was first summoned into the material plane by the imprisoned demonologists of the court of Elze in response to the promises of freedom from the masochistic Ecclesiastic King of Elze. This personal succubus was rune-bound to deliver exquisite pain to the king during his spare moments until he was slain by his subjects for neglecting his duties, free to visit her torments on anyone she deigned to notice. She is a member of the Court of Ristul, but she plans to take her position back from her brother B'Kor.
 * : Terrorblade is a demon marauder who is feared even by his own kin for doing all sorts of criminal acts in the Seven Hells. Imprisoned in the prison plane Foulfell and sentenced to a dreadful existence of twisted self-contemplation, Terrorblade gazed into the fractal walls of Foulfell and saw his worst self gazing back at him. Instead, he gained control over his inner demon and broke the prison walls, free to terrorize all of creation.
 * Maraxiform: This demon originated from the Sixth Hell and rose into the Hoven lands with the intent to conquer it. He fought against a mortal until he was driven back to the gates of Sixth Hell itself. Maraxiform was slain by Clinkz, but not before incinerating his killer's body and leaving him unable to die from the combination of his perpetual hellfire and an immortality spell that was cast on Clinkz upon their deaths. His head is now being used as a bow by Clinkz.
 * Eztzhok: Eztzhok is a demon who receives a share of the blood that Bloodseeker collects for his gods. At first, the Flayed Twins' servant merely wielded a pair of demonic blades resembling Eztzhok, but his features began to creep into the visage of Bloodseeker himself. The Flayed Twins reclaimed their loyal servant from the demon, but not without sacrifice.
 * Abzidian: Abzidian the Demon-Smith is renowned for creating the Demon Edge, a powerful sword whose blade is a shard of Radiant Ore and its hilt made of Direstone.
 * B'Kor
 * Anessix
 * Demons of the Cataract
 * Abyssal Horde
 * : The spirit of this demon was summoned was from the Outer Hells and into Warlock's Dreadwood staff, using it as a catalyst to summon its presence into the material plane. Terrorblade seems to be familiar with Warlock's demon.

Demon-possessed

 * : His disfigured form is the result of demonoplasty, the grafting of a demon's body parts into one's own body. Fusing the hand of his late demon partner into his left arm, his body was transformed into something unrecognizable, and the ever-consuming transformation has never stopped since that moment, slowly fusing the aspects of his late demon partner into his physical form and even his magics.
 * : He was once possessed by the demon Eztzhok until the Flayed Twins managed to reclaim him.
 * : While she doesn't possess any demonic features, her voice seems to be warped and she can speak Ozkavosh.