Typheus

Typheus, also referred to as "The Slumbering One", is the Denizen of the Land of Wind and Shade. According to the salamanders, he is kind of a huge dick (probably not literally). He lives in a palace that resembles a large pipe organ. He, like John, has the power to manipulate "The Breeze" and becomes enraged if he senses anyone else using it. Apparently he must be awakened by a special song that only the Heir of Breath can learn.

Typheus is responsible for 'putting a spell' on the fireflies, trapping them under the clouds. He was asked, in the past, to commission a bunch of Underlings. He also covered the planet with oil, which blocked some of the Parcel Pyxides.

Sleeping sounds were heard emanating from a large pipe in the area John first discovered. It is possible that The Slumbering One is currently deep underground. The Typheus of Greek myth, after being defeated by the Gods, was also trapped underground.

In an alternate timeline, John is killed because he fought The Slumbering One too soon, thanks to the advice of Terezi, and thus could not bring Jade into The Medium, most likely resulting in her death as well. Rose and Dave initially suspected that John's death was intentionally orchestrated by the trolls, and that it had been their intention all along. However, the plan was executed by Terezi alone, and the trolls were simply unable to contact an offshoot timeline. It's impossible to tell if Terezi tried to kill John despite the timeline, did it because she knew that she couldn't possibly succeed and wanted to mess with him, or realized killing John was the best way to ensure that Alternate Future Dave went through with the self-prototyping and created the current timeline. Nevertheless, she did appear to regret her actions after the fact.

It is later revealed in a shared dream bubble between the John that died in this timeline and Vriska that while he was tricked into doing this task, the act of dying was his own choice. He spoke with Typheus, who notes that while he isn't much to look at, he is not a bad guy at all. He learns that the timeline he is in is doomed anyways, and is given The Choice. While the first is never stated (likely just living out a meaningless existence), he takes the option to be killed by Typheus, which would spur Dave to go back in time and become Davesprite. John is shown to have scorch marks, implying he was burnt to death.

A dead, unprototyped enemy known as the "Typheus minion" is seen in the basement of Jade's House. This creature's relation to Typheus, as well as its cause of death, are unknown but was likely killed by Grandpa during his time in the game.

While the subject is never broached, it is possible that Typheus is also the Denizen of the Land of Sand and Zephyr, as Tavros shares John's title as the Hero of Breath in a similar pattern to Vriska and Rose, who share Cetus as the Heroes of Light, and Kanaya and Jade, who share Echidna as the Heroes of Space.

Trivia
There is a song that is for Typheus called, as stated by the composer.

In Greek myth, Typheus was a terrible snake-like monster that was one of the gods' greatest adversaries. He was called the Father of the Winds. This probably relates to how John's associated classical element is wind and his conflict with the Denizen.

Typheus' browser icon's snake part is green, just like Jade's typing color and John's Green Slime Ghost picture on his shirt.

It also should be noted that Typheus' minion ended up in Jade's house, whose typing color, coincidentally, matches his snake parts.