Editor's note: The following contains major spoilers for Stranger Things Season 4. There's a lot of mystery in the latest season of Stranger Things, with one character, in particular, causing a stir. The newest villain to the series, Vecna, is ruthless in his murderous ways and there's a lot of intrigue as to who it is. Well, we finally find out that Vecna's true identity is 001, but that leads us to ask: who exactly is 001?

When Eleven (Millie Bobby Brown) embarks on a journey to regain her powers, she is brought to Dr. Brenner (Matthew Modine) at his lab. It’s here where she is forced to watch back painful memories that she’d suppressed in the hope this will restore her lost abilities. Eleven discovers that reliving the horrors of her past and what occurred to her while under Papa’s care may help to recover the powers she’s lost. Eleven enters the lab's floatation tank and slowly begins to relive her forgotten past. This is where we first see the "friendly orderly," portrayed by Jamie Campbell Bower, a mild-mannered caring assistant. He explains to Eleven how he worked with 001 but doesn’t reveal what happened to him, increasing the mysterious aura surrounding the character. However, he does explain how One found his strength by reliving a memory where he felt angry, and Eleven takes this advice.

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Eleven finds herself in trouble when a group of kids at the lab attempt to overpower her in retaliation for her suppressing the most powerful boy there, but she’s helped by the orderly. He leads Eleven to a way out of the lab, but the tracking device in his neck means that he cannot leave with her. Unsuspecting of his true identity, Eleven rewards his helpful exploits by removing the chip for him. It’s then when he reveals himself to not just be the orderly: He is Number One.

We don’t know too much about Dr. Brenner’s experiments, but we find out this his very first test subject was a boy named Henry Creel. Born to Victor Creel (Kevin J. Johnson/Robert Englund), Henry demonstrates frighteningly powerful psychic abilities. Henry uses his powers to murder his mother and sister, murders which are then pinned on his father. After passing out from the sheer amount of power exerted on the killings, Brenner takes Henry into his "care" and takes control of him by placing the chip in his neck which suppresses his powers.

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Image Via Netflix

After Eleven frees 001 from the chip, he is now almost unstoppable and murders nearly everyone at the lab. Eleven's impressive powers are demonstrated here though as she is able to stop him.. She accidentally opens up a passage to the Upside Down and sends 001 into the alternate dimension. Years here take their toll and this is where he transforms into Vecna, the terrifying being that is now slaughtering people in the present-day Hawkins.

Vecna and Eleven have very similar abilities, with it being believed that 001 was the inspiration for all of Dr. Brenner's subjects. None of his subjects reached the same prowess of Henry though, but Eleven is by far the closest. Like Eleven, his abilities include being able to open up a portal between the two dimensions, allowing him to torment the people of Hawkins before killing them with his telekinetic powers. Volume 2 of Season 4 will hopefully reveal more about the latest villain, and what his plans for Hawkins might be. For now, we finally have answers to the questions about 001, and they're more spine-chilling than we could have imagined.