And Then, There Was Light
The issue begins with the Big Bang itself.
But before there was light, there was a darkness -- and the creature known as Knull lived inside this very darkness, comfortable and content. Everything changed when the light came and invaded his realm. The Celestials soon arrived, and it's then that Knull explains that the void which was once his got its name: space.
The cosmic giants arrived, waging war. With their light, Knull saw his own shadow for the very fist time, and he reached inside of its void to pull out a black blade, both liquid and solid at the same time. With this blade, he managed to fell a Celestial, severing its head. The rest fought back, and cast Knull back to the void. But he found refuge in the head of his victim and, in its fires, he began to forge his blade.
Knull explains that this blade was the very first, albeit crude, proto-symbiote. As he explains, this is where the symbiote's two weaknesses would be born: fire and sound. The fires of the Celestial Forge that melted it, and the heavy drums of the hammer that molded it.
But the real shocker comes when he reveals its name: All-Black, the Necrosword, aka the powerful weapon Gorr the God Butcher used to slay his victims in Jason Aaron and Esad Ribic's 2013 series Thor: God of Thunder.
In Thor: God of Thunder #6, readers discovered how Gorr came into possession of the Necrosword: it fell from the sky, along with two dead gods -- one dressed in gold, and the other in black. Gorr found the weapon at a desperate time, and used it to go on his vengeful rampage. In Venom #4, we learn that the black god who fell from the sky in Thor was in fact Knull, thus tying Venom intrinsically to Marvel's Asgardian lore as well as Spider-Man's. Though his connection to Thor is ancillary here, it's still a major moment in the Thunder God's history -- and the ties between the two aren't done yet.
After his fall, Knull spent centuries on the planet, learning to control what he calls the "living abyss," the darkness that flows out of him and that allows him to take control of other living organisms. As he grew accustomed to his abilities, Knull's power grew, with countless symbiotes now at his command. With them, he waged war across galaxies -- until he came to Earth, where he would clash... with Thor.