Marvel Comics Universe and Venom: First Host #1 Spoilers follows.
The Secret History Of The Venom Symbiote Revealed Before It Met Peter Parker The Amazing Spider-Man As A Symbiote In Secret Wars.
Although Venom’s first cameo was Amazing Spider-Man #299…
…and first full appearance was ASM #300.
Anyhow, turns out Peter Parker and Eddie Brock where not the first hosts of the Venom symbiote…
…it was actually a Kree Warrior named Tel-Kar.
He worked to free his people from teh Skrulls…
…and fought mightly.
He gave up the symbiote to be delivered to his superiors, but…
…due to engine troubles, the Kree needed their pilot who set to deliver the symbiote thereby…
…leaving the symbiote on that fateful ship that will…
…start his adventures with Earthlings.