'Stranger Things' Season 4 Part 1 Ending Explained: Who Is Vecna?

First it was the Demagorgan, then it was the Mind Flayer, but now Eleven (Millie Bobby Brown) and the residents of Hawkins have a much more menacing monster to face.

Vecna, as the creature is dubbed by Dustin Henderson (Gaten Matarazzo), is an all-new villain for Stranger Things Season 4 and it just might be the worst one they've faced yet.

From the monster's origins to its motivations, here is all you need to know about the new Big Bad in the Stranger Things universe, and how it relates to the first half of Season 4.

WARNING: This article contains spoilers for 'Stranger Things' Season 4 Part 1.

'Stranger Things' Season 4 Part 1 Ending Explained: Who Is Vecna?

Stranger Things
Main: Millie Bobby Brown as Eleven in "Stranger Things", Insert: Vecna, the new monster of the series. Netflix

The question that looms over the first half of Stranger Things' fourth season is who exactly Vecna is, and why the monster is terrorizing the town of Hawkins.

As the series progresses, Vecna begins his reign of terror, targeting individuals who have a deep, dark secret they don't wish to reveal to anyone else, and he uses horrific visions to twist the truth and inflict pain on them.

Vecna then transports his victims into their own makeshift hell where they are tormented by their inner demons as he hunts them down, though in reality the terrifying experience is all in their minds because the creature put them in a trance.

Once the monster catches them, as he inevitably does, Vecna kills them from the inside out by taking their soul while their body in the real world is broken in horrific angles and their eyes are gouged out.

At first it's not obvious why Vecna is choosing his victims, but that soon becomes clearer when viewers learn of his origins and motivations.

It turns out that Vecna has a more familiar origin story than fans might first expect and that's because of his link to Eleven.

You see, Vecna was actually once human and had special powers just like Eleven, in fact he is One (played by Jamie Campbell Bower), the first of Dr Martin Brenner's (Matthew Modine) test subjects.

Just like Eleven, he has psychokinetic and telepathic abilities that allow him to manipulate those around him, and he can also see into his victims minds and dig out their darkest secrets.

The show's finale sees Vecna's past revealed in two ways—through a memory of a conversation he had with Eleven and when he targets Nancy Byers (Natalia Dyer), with whom he shares his story through flashbacks while she's in a trance.

Vecna haunts Victor Creel's (Robert Englund) home because he was never a ghost tormenting the family, he is actually Victor's son.

In Eleven's memory she learns that as a child One saw humans as "pests" and he abhorred the idea of living a "normal" life and following the order and mundanity of everyday life, like having kids, going to work, and dying.

Becoming a Predator

Vecna needed more than that and so he started to test his abilities further in order to become a predator "for good," like with his beloved Black Widow spiders. He got stronger and stronger as he tormented animals of various kinds.

When his parents started to suspect something was wrong with their son they planned to take him to a doctor, except One refused to be put in psychiatric hospital and instead killed his mother and sister, and attempted to do the same to his father but fainted from overexertion.

It was Victor who was arrested for the murders and found guilty, and shortly thereafter One was taken by Dr. Brenner, who attempted to control him.

When that didn't work he put a chip in One's neck to stop him from being able to use his powers and started a program to make other children like him, such as Eleven, and it's only when Eleven removes this that he is able to unleash his wrath once more.

The massacre that's shown at the very beginning of the season wasn't carried out by Eleven, it was actually One who killed all the children and workers in the facility.

Rather than join One in his bid to destroy humanity, Eleven goes up against him, and using her powers she thrusts him into the Upside Down, making the first portal into the alternate dimension.

Then, as he was falling through the Upside Down, One became the creature Vecna after lightning struck him in such a way that it changed his skin and made him into the monster he is now.

Stranger Things Season 4 Part 1 is out now on Netflix, and Part 2 will be released on Friday, July 1.

Stranger Things
Millie Bobby Brown as Eleven in "Stranger Things" Season 4 Part 1. Netflix