The Walrider

"We have to contain it....."

- Chris Walker as he beheads a guard talking about stopping the Walrider from gaining a new host.

The Walrider, also known as The Swarm, is the main antagonist of Outlast, as well as the final enemy in the game. Later it reappears sporadically through Outlast: Whistleblower. It is behind the madness that seems to infect most of the inhabitants of the asylum and is the deity of the religion of Father Martin and his followers who adore it. It is first encountered at the beginning of Sewer level, after escaping from prison.

Outlast
The Walrider is seen multiple times throughout the game, its presence can be seen in the Courtyard scouring the air, as well as one encounter behind the locked gate. Project Walrider was the process of exposing patients to Morphogenic Engine Therapy to create a suitable vessel for the nanite swarm, for only a person that has seen enough horror can become the host. The aim was to create the perfect host for the Walrider, so that it could become a sentient being, as is evidenced by these notes: Gods and Monsters, Variant Postmortem. It is likely that The Variants are the results of this procedure.

Billy was capable of controlling the Walrider, with his self-directed lucid dream states, however because they were only using damaged and unstable minds to experiment on, the situation got out of control. The Walrider slaughtered everyone except one. Dr. Wernicke was kept alive by Billy all this time. When Miles reaches the Underground Lab, Dr. Wernicke, who was thought to be dead, instructs Miles to disable the power of Billy's life-support pod to undo what he has made, to murder Billy. After Miles shuts down the life-support pod, the Walrider, now without a host, attacks Miles and fuses itself with his body, taking him as its new host. As Miles limps towards the exit in pain, the door opens, revealing Dr. Wernicke and several soldiers. The soldiers open fire, but Wernicke realizes that Miles has become the sentient host. As the screen fades to black, the Walrider can be heard attacking as the soldiers scream in agony.

Outlast: Whistleblower
In Outlast: Whistleblower, the Walrider makes several appearances. In the Hospital, it will attack Waylon on sight in some areas. However, throughout most of the DLC, it is simply there for a visual effect and will not harm him. At the end of the DLC, (under Miles' control) the Walrider kills Jeremy Blaire in a manner similar to how Chris Walker was killed. At the end, the form of Miles inside of the swarm of nanites is visible from Miles' car, and moves towards the car. While starting the car and turning towards the gates, the Walrider pushes Miles' car and forces it through the locked gates.

Outlast: The Murkoff Account
"The word "Walrider" unleashed the full monetized wraith of the Murkoff Corporation."

- Pauline Glick

Although the Walrider uses Miles as a host, it seems that it still has the mind and emotions of Billy. After escaping Mount Massive, the Walrider heads to Nathrop, where Billy's mother Tiffany lived. Influenced by Billy's emotions, the Walrider stated to care for Tiffany in Billy's body. Unbeknownst to both Tiffany and the Walrider, Tiffany's house was under surveillance by Murkoff, who were searching for Waylon Park.

When Tiffany, who was seeing a truck driver, was hit by the man in rage, the Walrider manifested in the trucker's truck later and murdered him gruesomely. Upon finding the bloody truck, the Murkoff Agent opened the door to find the remains of the trucker, and the Walrider. Although he was slain by the Walrider almost immediately afterwards, the agent was able to warn Murkoff about the Walrider's location.

Knowing the threat they were facing, Murkoff immediately mobilized their forces, aware that they only had that one chance to eliminate the Walrider. They surrounded Tiffany's trailer with trucks carrying some kind of siphons. However, Tiffany refused to cooperate with Murkoff who had no way of forcing the Walrider to manifest itself. However, one of the Murkoff operatives, Pauline Glick, revealed to Tiffany that she was aware that Tiffany sold her son Billy to Murkoff although he wasn't even sick. Outraged by the revelation, the Walrider manifests itself directly before Tiffany and, claiming that he had trusted and loved her, rips Tiffany apart in rage. With the Walrider fully manifested before them, Murkoff activated the siphons which, once fired against Tiffany's trailer, succeeded in destroying the body of Miles Upshur. Although Murkoff believed the Walrider to be eliminated for good, Murkoff operative Paul Marion realizes that it had merely shifted hosts once again, escaping the scene inside a swarm of ants.

The ant swarm turns up at Temple Gate after the entire cult there has commited mass suicide. While Murkoff is busy with destroying all evidence, the swarm destroys the relay tower Murkoff used to send their brainwashing signals into the valley - ending the threat the tower posed to the sanity of those subjected to its effects.

Characteristics
While looking ghostly in nature, the Walrider is actually a swarm of nanites; small, nanoscopic machines who possess great strength and power. It took possession of Billy Hope. As it is shown by this document, when Billy was undergoing Morphogenic Engine Therapy, he learned to self-direct the lucid dream states, he was then capable of controlling the Walrider.

As it is composed of nanites, it is nearly invisible to human eyes, only showing a faint black aura. Miles can only see it clearly through the night vision on his camcorder. The Walrider has immense physical strength, and is the most physically powerful entity in the game. It can easily overpower any Variant, including the large, muscle-bound Chris Walker, as is seen in the Underground Lab when Walker is brutally murdered. When attacked by the Walrider, the result will be an instant death. The Walrider is relentless in its pursuit, while doors will slow its progress somewhat, it is capable of going underneath them.

Trivia

 * The Walrider is based off the nightmare creature from German folklore called ALP, who is also called "Walrider". Alp is said to originate from the mountains of Germany, similar to how the Walrider originated from Mount Massive. Both of them also have the ability to fly and turn partially invisible, as well as shapeshift.
 * Its most likely that the project was named after the myth.
 * The Walrider is considered a deity to Father Martin's religious cult.
 * The Walrider is considered the Primary antagonist of Outlast while Rudolf Weirnick and Jeremy Blaire were the Bigger Bads.