Venom is a man whose origins remain a mystery not just to local authorities but to historians everywhere, there are occasional and vague references to a man fitting his description dating as far back as written history, including both Aztec and Egyptian cultural references...
The origin story
A large part of the origin theory is very far fetches and there is a reason for it, the character was originally designed with the fantasy style background to add a sense of mystery to him, I am aware of how far fetched some of the origin tale is but hopefully you find it intriguing anyway.
Fact vs. Fiction
Details are sketchy at best as to the details but what we do know is that in the ancient world there was a reference to a sickness, not a virus, but a man referred to as a sickness and that he was gaining power, the powers of the time believed him to be a great threat, some of the ancient, its no secret that many ancient myths are based on real life figures, Hercules was in fact a man who lived, a man of incredible power but that is all he was, just a man, Anubis is another such figure they were only two of the brings responsible, another was a figure who is believed to be Voorhees, a long term rival of Venom. If the myth is to be believed the only way the powers were able to stop Venom was to have Voorhees merge his essence with that of Venom and then to lock them in a device that in legend became known as Pandora's Box.
The Tale of Pandora's Box
The tale of Pandora's box has always been a popular legend, over the centuries the story has been altered and changed into more of a religious tale as opposed to the truth behind the story, the version that lived today is that Pandora had been given the box by Zeus and instructed never to open it however had also been given the 'gift' of curiosity and ultimately opened the box letting out all of the evil into the world we see today but she closed it just in time so that hope still remained. Although the box's origin's are still to this day unrevealed there are manuscripts to confirm that the box's guard did have the label of Pandora, whether it was the name of the guard or simply a title given afterwards is unknown however she was the one responsible for opening it, it was open only long enough for part of their essence to escape which allowed Voorhees to return to the mortal plane, and it was closed in time to keep Venom inside, giving mortal kind hope, however what the manuscripts do not reveal is that through Voorhees and the merging of their 'essences' Venom was given a small amount of power in the form of temptation. He had enough power to tempt and ultimate manipulate men and women, it would take many centuries for it to pay off but eventually it would lead to his return to the mortal plane. His power over Voorhees however was limited at best only enough to block the knowledge of his presence.
THE RETURN OF VENOM
The hunt for Pandora's Box
There have been many figures over the history of man that have attempted to find the true origin of Pandora's box, some under the influence of Venom, others for their own ambitions but it would be a man by the name of Seth Jones (an enemy of Voorhees) that would discover it hidden away deep underground an ancient Aztec temple. He had plans to use it against Voorhees having being led to believe it was a way to kill him however Venom had influenced a high ranking man in the U.S. Secret Service, a mysterious man known only as General O'Connor. O'Connor had Seth Jones killed and took the box for himself.
The Box is opened
The box itself has many strange qualities however its most powerful is the way it appears to corrupt anything that comes into contact with it, whether it was the box itself of Venom influence is difficult to determine but this much is known, before the box entered O'Connor's posession he was an upstanding and honorable man, dedicated to serving his country, afterwards he became parinoid, greedy and self serving at the expense of anyone around him, the temptation became too much for him and instead of delivering it to his superiors as ordered he opened it releasing Venom. As a result the essences of Venom and Voorhees were merges once again however Venom had grown powerful over the centuries and he used the power to gain full control over Voorhees and release himself into the world.