Some fans had earlier theorized 001 was secretly the Mind Flayer of earlier seasons, given the creature's fascination with
001 is one of the most well-developed villains on Netflix's Stranger Things, and there's a lot to know about how he becomes so powerful.
As well as befriending Eleven in order to gain her trust so she would remove his Soteria implant, we learn in the final episode that 001 initially spared El because he wanted her to join him. He viewed her as an ally rather than an enemy because they were "alike".
In her rage, Eleven looks to disintegrate One, but instead sends him through to the Upside Down, opening her first gate to that other dimension. One bursts into flames as he is struck by beams of crackling energy, and ultimately becomes Vecna.
One and Eleven battled, and One ended up in the Upside Down, taking the form of the creepy demonic creature we now know as Vecna -- but still with his 001 tattoo. This is how the first portal to the Upside Down was opened.
While intending to get his revenge on Eleven and Brenner, Vecna also goes after victims who have dealt with traumatizing experiences in the past (reminiscent of his childhood and his time at the Hawkins lab).
"Vecna seems to be actually intrigued by Nancy being able to figure him out, to be able to get this close to the truth... I think this is more Vecna's narcissistic traits that pull him to Nancy, why he wants to give her this information."
Henry spends years trapped in the Upside Down, which changes him into the monster that is now terrorizing Hawkins in the present: Vecna. As Vecna, Henry uses his powers to torment his victims in the real world with haunting visions from their pasts before ultimately possessing them and mangling their bodies.
After previously having tricked Eleven into destroying the chip, Peter goes on a killing spree in the lab until a confrontation with Eleven ended in her casting him into the Upside Down - where after falling through various dimensions and sustaining various injuries, Peter was transformed into Vecna.
Vecna was not always a hideous beast of the Upside Down. He was once a troubled child in the real world named Henry Creel. Henry's “problems” caused his family to move to Hawkins in 1959. However, the exact issues that led to the relocation are unclear.
For whatever reason, he identified Eleven as the likeliest target for his manipulations and got her to remove a device Brenner had implanted in his neck. The device (called a "soteria," which we explained in our analysis here) had prevented Henry from using his powers or escaping the lab.
On a psychological level, such trauma, combined with Eleven's young age, would have had a detrimental effect on her mental health - meaning the suppression of these horrific memories was a completely natural reaction.
At his empire's height, Vecna was betrayed and destroyed by his most trusted lieutenant, a vampire called Kas the Bloody-Handed, using a magical sword that Vecna himself had crafted for him, now known as the Sword of Kas.
However, within the red smoke of Vecna's Mind Lair, it wasn't the song itself that saved her, but the memories it conjured up. What broke through to Max was the happy, loving memories of her friends, particularly Lucas and Eleven, and these were what truly allowed her to break free of Vecna's grasp and escape.
Vecna hated humanity, believing human beings had imposed an artificial order upon the natural world.
This also perfectly explains why Vecna's Upside Down spot is the Creel House. It is the place where he discovered his “purpose” and he can hang out there with his deadly spiders and gain strength from taking lives.
In his twisted mind, Vecna believes that he his helping the world by wiping out humans, as a "predator, but for good." When Vecna asks for El to join him, it's because he also sees her as a predator, "better" than humans. He offers her his path as a sort of freedom, as they reshaped the world in their image.
Netflix Vecna has plans for world domination. Essentially, Vecna hates humanity, and wants to take over their world. He had hoped that Eleven would help him achieve this goal. But when he realised she wouldn't, Vecna instead used her.
(All of which have been cited by show creators the Duffer brothers as inspirations for the villain.) But he does have a surprising weakness: music.
Next up, the viewers go on to theorise that One/Vecna is actually Eleven's dad. Yep, told you it was wild. The theory claims that Brenner wanted to create a child with stronger powers, so he waited until One was old enough to become a father.
Using his supernatural psychokinetic abilities, Vecna can probe and influence the minds of others. Motivated by a cruel and misanthropic philosophy, Vecna targets particularly traumatized, mentally ill or insecure individuals.
The theory predicts that Vecna wants to regain his human form, and he will use Will to do so in Season 5. Knowing that Vecna singled out Will in Season 1, it's a reasonable theory, but it might go too far. After all, Vecna already has a human form, and he has vowed to eliminate humanity.
Eleven defeats Vecna (Jamie Campbell Bower) in a psychic battle, Steve and Nancy light his body on fire, and Nancy shoots him several times with a sawed-off shotgun. But it's not enough. Vecna's body goes flying out the window of the Upside Down Creel house and he lands with a thud.
1. Is Nancy OK? Yes! Nancy (Natalia Dyer) is fine — at least, as fine as she can be after being traumatized by Vecna (Jamie Campbell Bower) and almost strangled to death by his squelchy, squelchy tentacles. Instead of escaping Vecna's Mind Lair by hearing her favorite song, Nancy is actually released by Vecna himself.