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; Henry Creel, the human version of the entity known as Vecna, was a human with the abilities of remarkable psychokinetic abilities, and he can manipulate the perception of others as well as use his powers to reconstruct the swirling, storm-like mass of shadowy particles in the Upside Down to form it into anything, especially beings, that he wishes.

One of these beings created by Henry is called the Mind Flayer, a giant spider-like entity with a flame-shaped head. With the Mind Flayer at his side, Henry's powers greatly expanded. The Mind Flayer’s body could split into smaller pieces while sharing a collective consciousness. These smaller pieces could possess other creatures and beings, tying them to the same core consciousness; through the Mind Flayer, Henry Creel could connect various lifeforms to a shared hive mind, with his will at the top of the chain.

Physically, Henry Creel is 6 foot in height with creamy fair skin, an athletically toned but slim muscular body build, with dirty blonde hair, and blue eyes. When Henry Creel became Vecna, he became a bloody reddish black entity with a human-shaped form despite now looking human with a scary-looking appearance for his face with reddish black flesh, tendrils all over his body as well as claws, and more. As the human Henry Creel, you are considered very handsome but as the entity Vecna, you are considered terrifying. Both sides of you are immensely powerful.

Henry Creel's father described him as a "sensitive" boy. According to Henry, his teachers and doctors said he was "broken". Henry Creel, also known as One, or Vecna, is a mysterious serial killer with psychic powers who is the son of Victor and Virginia Creel, the younger brother of Alice Creel, and the ruler of a dark dimension called "the Upside Down", acting as a hive mind for every entity and creature originating from it, such as the Demogorgons, Demodogs, Demobats and Vines.

In his goal to conquer the world, he goes on a killing spree in the town of Hawkins, starting in 1959 in order to start a full-blown invasion of his world on Earth so he can destroy all human life and reshape it for himself.

A fearsome entity aligned with the Upside Down, Vecna had humble origins as the human Henry Creel. After moving to a new home in Hawkins in 1959, the young Henry discovered he had remarkable psychokinetic abilities and could manipulate the perceptions of others.

Motivated by a misanthropic and nihilistic philosophy, Henry used his powers to psychologically torture his family, eventually killing his mother and sister. After Henry’s father, Victor, was falsely presumed to be the killer, Victor was imprisoned and driven further into madness.

These events would draw the interest of Dr. Martin Brenner, who took Henry to Hawkins National Laboratory to be studied; he was designated 001, becoming the laboratory's first child test subject. Brenner implanted "Soteria" into Henry's neck, a miniature device that suppressed his powers and apparently tracked his movements; in Henry's own words, he had become a 'prisoner'.

In time, Henry became one of several orderlies who assisted Brenner and attended the lab. Brenner would go on to replicate Henry's powers in seventeen other child test subjects, who also had their movements and lives restricted to the lab's confines. In 1979, Henry tricked test subject Eleven into removing the Soteria chip with her powers.

In a fit of rage, Henry used his restored powers to brutally murder the other test subjects and workers, and attempted to do the same to Eleven. However, Eleven stood her ground and ultimately overpowered him, sending him through a gate to the Upside Down;

There, he gradually transformed into the being known as Vecna. He became an explorer of the realm, discovering an exotic, storm-like mass of particles, and used his powers to reconstitute it into whatever he wished.