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.
Knull, the God of the symbiotes, decides he doesn’t much care for the various other deities now inhabiting the burgeoning Marvel Universe. Armed with his symbiote suit and symbiote sword, he embarks on a campaign of deicide, but bites off more than he can chew.
Crash-landing on an alien planet, Knull loses All-Black the Necrosword, and it’s picked up by a local, who gains both its abilities and its hatred of deities. This individual becomes known as Gorr the God Butcher, one of Thor’s greatest enemies.
Speaking of Thor, Knull encounters another enormous setback when he comes into direct conflict with the God of Thunder. After losing All-Black, Knull switches to a strategy of sending symbiotes out into the universe to conquer planets. However, Thor defeats the symbiotes so soundly on Earth that Knull loses control of them.
Freed from Knull’s control, the symbiotes turn on their former master. Having absorbed some positive personality traits from various hosts, the symbiotes decide to take down their malevolent deity, and millions of them use their own biomass to imprison Knull within an artificial planet.
The symbiotes name the construct “Klyntar,” after their species’ word for “cage,” and that moniker eventually becomes the name of their race. Several hundred generations later, the Venom symbiote is born on Klyntar.
For reasons that remain unclear, the Venom symbiote is cast out of Klyntar society and is captured by an exploratory crew of Kree. The warrior aliens experiment on the young Klyntar. After discovering its symbiotic nature, they decide to bond the Venom symbiote with one of their greatest soldiers, Tel-Kar.
Armed with the most famous alien suit in all of Marvel Comics, Tel-Kar becomes a legend in the Kree-Skrull War - a centuries-long conflict between the two alien races that would one day impact the Earth and its mightiest heroes.
Tel-Kar - the first host of the Venom symbiote - uses his alien suit to great effect in the Kree-Skrull War, but he eventually loses the Klyntar in an alien prison. The symbiote remains in captivity there for a lengthy period, until the prison becomes part of “Battleworld” - a composite planet cobbled together by The Beyonder, the immensely-powerful being behind the Secret Wars.
In the publisher’s first major crossover, several Marvel heroes and villains, including Spider-Man, are transported to Battleworld to test their might.