A fearsome entity aligned with
In episode 7, Vecna is revealed to be Henry Creel (played as a youngster by Raphael Luce), the son of Victor Creel (Robert Englund) and his wife Virginia (Tyner Rushing) shown in the 1950s flashbacks.
From the beginning, Vecna was a long-vanquished lich—a wizard who used dark forbidden magics to keep themselves effectively immortal but in a perpetual state of undead decay—and while DMs were free to use their imagination and flesh him out into a proper villain, his only official existence in the old D&D books was as ...
According to the helpful folks over at the Dungeons & Dragons Forgotten Realms fandom wikipedia, Vecna was once a human king who became a lich (a powerful undead wizard).
The final scene of Volume 1 shows a shot of Vecna, and a close up of the 001 tattoo on his arm, confirming that Henry Creel, a.k.a. Number One, became Vecna.
Vecna's first big credited kill was Chrissy Cunningham (Grace Van Dien). He followed that murder with canonically terrible driver Fred Benson (Logan Riley Bruner) and basketball star Patrick McKinney (Myles Truitt).
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.
Vecna's obsession with time appears to be linked to his hatred of humanity. He views time as a human imposition on the natural world; an attempt to impose order on nature.
Eleven has a memory during this episode and realizes that 001/Henry Creel (Jamie Campbell Bower) wants her to join him on his evil journey, and she banished him to the Upside Down. 001 then transformed into Vecna, the horrifying Stranger Things villain.
Realizing he had tremendous psychic power, he haunted his family with visions before ultimately killing most of them. His father was framed for the murders and locked away in a mental hospital as a disturbed serial killer. Henry then found himself in the care of Brenner, who decided he wanted more kids like the boy.
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 is the Mind Flayer. The Mind Flayer is Vecna. Vecna (Jamie Campbell Bower) has a connection to the very beginning of 'Stranger Things.
She opened a portal to the Upside Down, which sucked Henry Creel in. There the dark mirror world ripped apart his skin as it began to remake him into something sinister and twisted. But it was a transformation Henry Creel welcomed.
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.
This is a reference to the D&D character Vecna, for whom this Vecna is named; the D&D Vecna has a monstrous hand infused with dark magic. The design of Vecna's hand is also a nod to Freddy Krueger, the Nightmare on Elm Street villain who had a huge influence on this season in general.
Orcus, the demon prince of undeath, taught Vecna a ritual that would allow him to live on as a lich. Beyond death, he became the first and greatest of all liches.
"I walked up to her [as Vecna] and she burst into tears. She wouldn't look at me and she was visibly just disgusted by the whole thing... After she cried and I made it obvious that she knew it was me, one of the things she said was that, 'I knew it was you when I could smell cigarettes,' because I'm a smoker."
Sharing more about Eleven's real father Andrew Rich could be a great way to wrap up the story.
Played by Jamie Campbell Bower, each prosthetic was glued to his skin with medical adhesive by prosthetics designer Barrie Gower and his team. For the finishing touch, Vecna was covered in "glossy slime to make him really, really glossy and wet looking," according to Gower.
This is because his trusted accomplice, Kas the Bloody-Handed, betrayed him and used the sword Vecna created himself to chop off his left hand and remove his left eye. This ultimately destroyed Vecna. Though they're clouded with cataracts, Vecna in Stranger Things has both of his eyes.
His method of killing is ritualized. Vecna started twisting bodies and removing eyes before imprisonment in the UD to fuel its own individual power. It takes the eyes to help hold the souls in darkness and because it did not wish to be observed.
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.
Brown is likely right in saying that no one created the Upside Down and that the parallel dimension has always existed. And if the boys' science teacher was right in saying there are “infinite variations” of our world in alternate dimensions, there could even be several versions of the Upside Down out there.