The Tuurngait is a sentient extraterrestrial being residing in the shelter, that was discovered by the Archaic excavation team led by Philip's father, Howard LaFresque. It has a hive-mind intellect that it manifests in "The Infected ", which are humans that are transformed into intelligent zombies to serve the Tuurngait.
Long before the arrival of the Archaic, the Tuurngait was worshipped by the Inuit, who believed it to be a benign spirit. However, when it was disturbed by the Archaic researchers, it spread itself through the ranks of the Shelter and turned them into husks that housed the Tuurngait's will within them. It tells Phillip at the end of Black Plague that it wishes no harm to humans, only wanting to be left alone. However, there are no signs that the Archaic actually wished harm to the Tuurngait, despite its claims to the contrary, and the notes found by the player all state that the Tuurngait virus was unleashed immediately after the discovery of the ruins.
This means that it's very possible that the virus was attempting to manipulate Phillip, which would explain why the monsters attempt to kill him throughout the series, despite the Tuurngait's statements that it wishes no harm. Left unexplained are the reasons that the Tuurngait felt it neccessary to kill Clarence instead of simply reintigrating him, or why the animals in the first game were of lesser intelligence, according to Howard. The worms and spiders aren't explained either, but it seems likely that they were infected by the Tuurngait far earlier than when the Archaic set up shop there and mutated over time to fit its needs. Lastly, at the end of Black Plague Philip seems to be succumbing to some form of infection, despite the Tuurngait's assurances that he was 'stronger' than Howard.
The Tuurngait's origins are unknown, remaining so throughout the series...
Tuurngait is actually part of Inuit Mythology
Some spirits were by nature unconnected to physical bodies. These figures were called tuurngait (also tornait, tornat, tornrait, singular tuurngaq, torngak, tornrak, tarngek). Some were helping spirits that could be called upon in times of need. Some were evil and monstrous, responsible for bad hunts and broken tools. They could also possess humans, as recounted in the story of Atanarjuat. An angakkuq with good intentions could use them to heal sickness, and find animals to hunt and feed the community. He or she could fight or exorcise bad tuurngait, or they could be held at bay by rituals; However, an angakkuq with harmful intentions could also use "tuurngait" for their own personal gain, or to attack other people and their tuurngait.
Though once Tuurngaq simply meant "helping spirit", it has, with Christianisation, taken on the meaning of demon in the Christian belief system.
Tuurngait ArtifactsEditStrange Artifacts scattered across the game are actually Tuurngait artifacts. Dr. Amabel Swanson said that those strange artifacts can spread the virus. Artifacts origins are unexplained fully.
These strange artifacts can be collected and when you found them all — in the end of the game, you will unlock the secret password for secret developer stuff and a secret game called Schmup.
PS: You have to use secret password on the super_secret.exe
Strange Cylindrical Artifacts are to be seen in the three Penumbra games, and Amnesia: The Dark Descent. These artifacts are Tuurngait in origin, and, in Penumbra, save the game when clicked. They are thought to absorb the memory and flesh of humans who touch them. They also resurrect Philip if he dies.
Their origin is mostly unknown; however, it's possible that they do not exist, or at least do not have the effect of reviving Philip, within the canon universe, as Philip isn't resurrected after the end of Penumbra: Black Plague.
In Amnesia: The Dark Descent, several remarkably similar artifacts exist scattered throughout the castle. Instead of saving the game, however, they play back pieces of Alexander Von Brenenburg's thoughts.