Most Marvel Comics fans assume they know the gist of Venom’s backstory, but the character's origin is more complicated than many readers realize. Venom's gooey black costume is actually an alien symbiote known as a Klyntar, and it needs to form a symbiotic relationship with a host body to thrive.
It isn’t until this particular symbiote pairs up with Eddie Brock that the symbiotic fusion takes on the name “Venom,” but Brock is far from its first host. The Venom symbiote had a lengthy series of adventures and partners before encountering Peter Parker - or any other Earthling - and the entire tale of the Klyntar race is one that goes back billions of years.
Fans of Spider-Man who are unfamiliar with Marvel Comics continuity might think they have a pretty good grasp on the Venom symbiote thanks to multiple adaptations of its origin - including in the '90s animated series and the much-maligned Spider-Man 3.
The basics are always the same. The symbiote arrives from space, finds Peter Parker, and grants him additional abilities on top of his amazing spider powers. Eventually, the symbiote’s violent tendencies become apparent, and Spidey separates from it. The symbiote then merges with Eddie Brock to form Venom, one of the wall-crawler's greatest enemies. The real backstory is much, much more complicated.
To fully understand the origins of the Venom symbiote, one has to go back billions of years. The story begins with Knull, an immensely powerful deity who is older than the universe and whose powers are diverse and immense.
Little is known about Knull's origins, but we do know he was around when the Marvel Universe consisted only of darkness - and that he wasn’t exactly pleased when that started to change.
The Celestials are some of the most powerful entities in all of Marvel Comics. They're timeless beings responsible for the creation of the multiverse itself. Knull doesn't like the Celestials bringing light into his dark corner of existence, so he wages war against them.
To aid him in combat, Knull creates a weapon - All-Black the Necrosword - out of the dark energies of his own shadow. Not only does All-Black become one of the most influential items in the Marvel Universe, but it also gains sentience, making it the first of the symbiote race.
In his battle against the Celestials, Knull uses All-Black the Necrosword to decapitate one of them. In the process, he creates Knowhere - an important setting in the Guardians of the Galaxy series - and establishes himself as a truly cosmic threat.
Knull turns Knowhere into his base of operations and uses its internal energies to improve his symbiotic weapon - forging a suit of armor in the process. This symbiotic suit is the precursor of all future symbiotes and establishes the basic traits of the gooey alien race.