Eldwurms

Eldwurms are very old and powerful dragons. While fearsome, eldwurms are also long-lived, and have accumulated much wisdom in their years. They were also renowned as scholars and historians, with their history recorded in numerous eddas and epics. However, the decline of their numbers also led to a stagnation in their literature, with very few additions since their golden age.

Literature
The dragon scholars write many kinds of texts, including the Eldwurm Eddas, verses, sagas, etc. In these works of art, these otherwise fearsome beasts express their wisdom and literacy with each line of text that they write.

The Eldwurms' sagas speak of an "ill-aspected essence" (known as wraith energy) that certain dark souls release upon death, and what revenants and untethered spirits use to take on a form that would allow them to walk the earth. If one were to part this essence from the aforementioned spirits, condense and collect a sufficient quantity of it, and then shape one's self from it, they could become a being that is similar to a wraith. One being has already attempted this process, but their name and existence has been lost to history.

In their search for knowledge, ancient eldwurms have found and learned techniques to resist death and prevent the loss of one's life.

In Dota: Dragon's Blood
Unlike the Eldwurms of the main games, the Eldwurms in the story of Dragon's Blood are more cosmic than mundane and have a significant role in the existence of the infinite macrocosm; their souls sustaining the balance and the existence of countless universes, the pillars of chaos and order, the Manifold Forms, and even nothingness itself, all of them going into disarray and destruction should their be released from their "corporal fetters". Because of this, they are also known as the Pillars of Creation.

Eldwurms are not mere old dragons but they are the embodiments of the four classical elements and the four fundamental forces. They all exist in an unknown plane of existence that seems to be higher than the material plane, and their souls descend from that very plane to embody the respective dragons that are their physical aspects, such as Slyrak descending into the body of a fire dragon. Upon death, their souls simply reincarnate in another dragon, usually the oldest one that they can find, in an endless cycle of life and death. The Eldwurms refer to their physical forms and avatars (the dragons and anyone they may possess) as "flesh illusions" further implying that their physical appearances are mere avatars.

When their "flesh illusions" go to sleep, their souls ascend back into their plane of existence, rejoining the Thunder, where they become aware of all the dragons of their type, being able to perceive whatever these dragons sense and interact with even if it's from a mere body part of their corpses being used. From there, the Eldwurms sing their song, a song that cannot be expressed through voice or instruments, which is a measure of the stability of the world that they support with their existence. If they do not sing, or if there is a missing singer, then there is clearly something wrong with the stability of the cosmos.

Elemental Eldwurms

 * Slyrak: The Father of Fire, Ember Eldwurm. Slyrak embodies the scorching phenomenon of fire in the form of the fearsome fire dragon species.
 * Aethrak: The Air Eldwurm. Aethrak embodies the ethereal forces of wind in the form of the raptor-like air dragon species.
 * Lirrak: The Mother of Oceans and Storms, Water Eldwurm. Lirrak embodies water in all states of matter (even ice) in the form of the aquatic water dragon species.
 * Uldorak: The Earth Eldwurm. Uldorak embodies the gritty, physical matter of the material plane in the form of the subterranean earth dragon species.

Fundamental Eldwurms

 * Vahdrak: The Father of Chaos, Chaos Eldwurm. Vahdrak embodies the unstable powers of chaos and darkness in the form of the eldritch chaos dragons.
 * Orrak: The Luminous Eldwurm. Orrak embodies the brilliant powers of light in the form of the luminous dragons.
 * Indrak: The Father of Lightning, Ionic Eldwurm. He who deals in objective facts and speaks only truth, Indrak embodies the electric charge in the form of the wise ionic dragons.
 * Byssrak: The Void Eldwurm. Brief with his speech, Byssrak embodies the unknowable force that warps the structure of spacetime in the form of the rare void dragons.