A trio of the child, adult, and old unknown arrive in the Sic Mundus headquarters in 1987, taking the blueprints for the Apparatus and setting the room on fire. They proceed to Bernd Doppler's house, where they kill him and take his set of master keys of the Winden Nuclear Power Plant. The Unknown subsequently break into the power plant at night and search through Claudia Tiedemann's records, finding the disappeared director's secretary and killing her.
After Gustav Tannhaus receives time travelers in 1888, he sets off to the nearest large city to spread word by telegram. To prevent this, the Unknown stop the carriage and kill the old man. They visit Eva at the Erit Lux headquarters, bringing her items from Adam's World, such as a diagram of the control system at the power plant, H.G. Tannhaus's book Ariadne, and a pocket-watch engraved with "For Charlotte."
Returning to Adam's World, the Unknown meet with Tronte Nielsen in 1954, with the adult Unknown claiming he gave the boy his name and knew his mother Agnes. He gives Tronte the ouroboros bracelet as he leaves. They then meet Doris Tiedemann at the Winden church, talking to her about Agnes and claiming that he used to be a pastor. He reveals that Doris's husband Egon is cheating on her, causing her to leave him. Finally, the trio approach the mayor of Winden, forcing him to sign the permit for the power plant at gunpoint after the coal lobby blocks it. He closes the notebook at the Erit Lux headquarters, revealing himself as the author of the notebook recording all mysterious events in Winden.
In 1986, the trio trigger a nuclear accident by entering the volume control room and simultaneously opening a valve, creating nuclear waste that is later stored in barrels, as well as the God particle responsible for the Apocalypse in both worlds.
In Eva's World, Eva explains to Martha that she is pregnant with the Unknown, which Eva believes to be the origin of all life. The child Unknown goes to hug Martha. However, Claudia Tiedemann discovers the true origin in the Origin World that was destroyed to create Adam and Eva's Worlds, After Jonas and Martha prevent the deaths of Tannhaus's family and the inciting incident that created the two worlds, its residents cease to exist, including the Unknown.
- Dark Season 3 Episode 1: "Deja-vu"
- Dark Season 3 Episode 2: "The Survivors"
- Dark Season 3 Episode 3: "Adam and Eva"
- Dark Season 3 Episode 4: "The Origin"
- Dark Season 3 Episode 6: "Light and Shadow"
- Dark Season 3 Episode 8: "The Paradise"
- The adult and old versions of The Unknown are played by real-life father and son.