Denizen

The Denizens are immensely powerful NPCs, one of which is found in each of the four lands. They are, at first, asleep, but as the player progresses through the Seven Gates, they awaken. Each is said to guard an immense Grist hoard, to be released upon their defeat and used for the Ultimate Alchemy, though Davesprite says that he "had no idea how the denizens worked at all", implying that they serve another purpose. This is probably related to "the choice" each Denizen will offer their opponent and the fact that they are capable of conversing with the players. The Denizens control the underlings and are responsible for many of the problems found on the players' planets.

The Trolls fought denizens of their own, as they are an integral part of the game and its often ignored "plot", but presumably they all (except for Kanaya and potentially Tavros) killed them quickly before the denizens could talk to them. Evidence suggests that Denizens may be tied to a player's aspect as the trolls' and the kids' sessions share at least two Denizens, namely Cetus and Echidna, who were the Denizens of both Heroes of Light and both Heroes of Space. However it remains unconfirmed and is unknown if this holds true for the Heroes of Time, Heroes of Breath, Heroes of Life and Heroes of Void.

Typheus


Also referred to as the "The Slumbering One", Typheus is the Denizen of the Land of Wind and Shade. He is the Denizen of John, and likely Tavros as well, making it the Denizen of the Land of Sand and Zephyr.

In Greek myth, Typheus was a terrible monster that even the gods feared, and after he was defeated, was trapped underground. (Specifically, under Mount Etna, the volcano Hephaestus was said to reside in.)

Cetus


The Denizen of the Land of Light and Rain in the kid's session and the Denizen of the Land of Maps and Treasure in the troll's session. As such she is the Denizen of both Heroes of Light, Rose and Vriska.

In Greek myth, a Cetus was a large fish, serpent, whale, or sea monster, which would explain all of the fish being eaten, and why the Trolls' version of Cetus was found amidst shipwrecks.

Hephaestus


The Denizen of the Land of Heat and Clockwork is Hephaestus, lord of the forge. He is the Denizen of Dave and likely Aradia, making it the Denizen of the Land of Quartz and Melody.

In Greek myth, Hephaestus lived in a volcano, and was the God of blacksmithing.

Echidna


The Denizen of the Land of Frost and Frogs in the kid's session and the Denizen of the Land of Rays and Frogs in the troll's session. As such she is the Denizen of both Heroes of Space, Jade and Kanaya.

In Greek myth, Echidna was considered the mate to Typheus and the "mother of all monsters" in that she actually gave birth to them.

Hemera
The Denizen of the Land of Crypts and Helium in the post-Scratch session. She is the Denizen of Jane, a Hero/Noble of Life, and therefore possibly also the Denizen of Feferi and the Land of Dew and Glass in the troll's session.

In Greek Myth, Hemera is considered to be the personification of daytime.

Nyx


The Denizen of a currently unknown land in the post-Scratch session. She is likely the Denizen of Roxy, a Hero/Noble of Void, and therefore possibly also the Denizen of Equius and the Land of Caves and Silence in the Trolls' Session.

In Greek Myth, Nyx is considered to be the personification of nighttime.

Yaldabaoth


The Denizen of a currently unknown land in the post-Scratch session. He is likely the Denizen of Dirk, a Hero/Noble of Heart, and therefore possibly also the Denizen of Nepeta and the Land of Little Cubes and Tea in the Trolls' Session.

In Christian Gnosticism Yaldabaoth ("Son of Chaos" in Hebrew) is the demiurge, a being who was responsible for the creation of the universe. Yaldabaoth is the only known Denizen who is not a figure of classical Greek mythology, though the concept of a 'demiurge' was originally derived from the Platonic dialogue, Timaeus.

Trivia
The Denizens of each kid match up with their respective browser of choice, implying that they may share appearances with these browsers' icons, but at least their minions should. Echidna's browser icon has a white human torso with breasts and head (perhaps, lacking arms) with two snake tails on its bottom; Typheus' has a white torso with head and a snake tail on its bottom; Hephaestus' browser icon version is engulfed in flames, but seems to have a black torso and black head and would be humanoid, making him most human (perhaps, because in Greek myth he was god of blacksmithing and was a human-like god), and Cetus' has a fish body with a white human-like head. This would relate to Rose Lalonde's strong connection with The Noble Circle of Horrorterrors and her least human and most reckless actions in the game (her plan to blow up the Green Sun and her going grimdark), as a foil to Dave's, who was mainly gathering money to buy fraymotifs.

Each browser icon has a coloured part that matches its user's normal clothing: John's Green Ghost Slime and Typheus' snake part are green, Jade's depictions on her shirts are blue like Echidna's lower half, Rose's Horrorterror picture on her shirt is purple, like Cetus' icon, and Dave's record has a red part, like Hephaestus' flames. Nothing associated with Jane matches Hemera's coloring, but her clothing does appear to match the colour associated with Dirk Strider.

Each of the Denizen's lairs are also marked with the same browser icons, at least, Hephaestus' and Typheus' are, thus indicating that the homes of Cetus and Echidna are probably marked the same way.

To date, Jake's desktop has not been seen at all, so his (and presumably Eridan's) Denizen is also not yet known.

In the ancestors' session, Aranea was the player who consulted Echidna to carry out the Scratch. Although the default assumption would be that Echidna was likely the denizen the ancestors' Space player, it is not certain; one possibility is that instead of players of the same aspect having the same denizens, the matching of denizens when comparing the ancestors' session to the trolls' could be by class, as both Kanaya and Aranea are Sylphs. This would conflict with how Jade, the Witch, has Echidna as her Denizen. It's also possible that Denizens are not restricted to solely interacting with their Land's player, as shown by how Davesprite, after time travelling to the alpha timeline, was offered a Choice by Hephaestus.