A 1959 flashback in the mid-season 4 finale reveals a 12-year-old One (Jamie Campbell Bower). That puts One, a.k.a. Vecna, as 24 when Eleven was born.
1959: Twelve-year-old Henry Creel murders his mother and sister. Henry's father Victor is imprisoned for the crimes. As he later confessed to Eleven, Henry (AKA "One" or "Vecna") realized he had psionic powers (telekinesis, mind-control, the ability to make people see visions) when he was a young boy.
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.
Well, Vecna is One, who is Henry Creel. As a child, Henry was ostracised for being different, and had strange powers.
Birth and early life
Henry Creel was born in 1947 to Victor and Virginia Creel, and had an older sister by three years named Alice. He did not fit in with his peers; his father described him as a "sensitive" boy.
After taunting her with incessant chiming from a grandfather clock and appearing before her in hallucinations, Vecna eventually kills her in an incredibly gruesome way. First, she went into a trance with her eyes rolling into her head, then she began to levitate before her eyes were removed and bones were snapped.
His first victim was Chrissy Cunningham. Vecna targeted Chrissy by using her depression and eating disorder against her in his visions. Chrissy was killed in Eddie Munson's trailer, and the first gate was opened on the ceiling.
In the D&D realm, a defining feature of Vecna is that he's missing his left hand and left eye. 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.
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). But wait, there's more.
Vecna draws power from sad and angry memories and that is the main reason he targets traumatized teens. Those teens are a well of power just there to be absorbed. This is not just a theory, Vecna himself told Eleven about the power that angry and sad memories hold.
He didn't name himself Vecna, the kids did. They named him after a DnD character who's a wizard, since Vecna's curse sounds like something a dark wizard would do.
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.
Vecna was the original child studied by Dr. Brenner and the son of Victor Creel. He's the infamous Number One, but had his powers blocked and worked as an aide in the Hawkins National Lab.
The episode then cuts to Vecna in 1980s Upside Down, zooming in on his arm, where a tentacle slides away to uncover 001 tattooed on his wrist. So Vecna is 001, who is also Victor Creel's son.
Brenner (Matthew Modine) states in the Stranger Things episode "Papa" that Vecna "consumes" everything about his victims, Vecna targets traumatized victims because it builds for him a well of sad and angry memories to draw from. With each victim, he can become gradually more powerful.
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.
Season 4's main villain Vecna contains a multitude of easter eggs. To start, he has a giant, claw-like left hand. 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.
Among Vecna's staunchest foes are Kas, Iuz, Saint Cuthbert, the Lady of Pain, Pholtus, and the Circle of Eight. He is also opposed by the Old Faith and the Silent Ones.
Arkhan grappled the Hand. Percy had considered shooting it off, but it couldn't be done. When the party defeated Vecna and banished him, the Hand once again remained. Arkhan pretended to prepare to destroy the Hand, cut off his own left hand, somehow attuned to the artifact in an instant, and used it to Teleport away.
Everything on Stranger Things leads back to One, a.k.a. Henry Creel, a.k.a. Vecna (Jamie Campbell Bower).
Vecna prays on those dealing with trauma, which is why Max, who recently lost her brother, Billy, was the perfect victim. While she initially got away from him with help from her friends and her favorite song, she wasn't as lucky at the end of the season when Vecna captured her again.
"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."
Seeing Stranger Things' Vecna Made Millie Bobby Brown Cry
She's a 10, but she cries when she sees Vecna? She's an Eleven.