A symbiote is a fictional extraterrestrial organism in Marvel Comics. Sometimes referred to as a "living costumes" because of the way the amorphous creatures depicted as enveloping their hosts.
The first appearance of a symbiote occurs in Amazing Spider-Man #252 in which Spider-Man brings one home to Earth after the Secret Wars (Secret Wars #8, which was released months later, details his first encounter with it). The concept was created by a Marvel Comics reader , with the publisher purchasing the idea for $220.00. The original design was then modified by Mike Zeck, becoming the Venom symbiote. . The concept would be explored and used through out multiple storylines, spin-off comics, and derivative projects.
The back-story to the concept of the symbiotes has never been clearly established. However some stories have shown that their species existed for millions of years prior to the arrival of the Venom symbiote on Earth . It is implied that Galactus, devourer of worlds, consumed a world which they had taken over and where they had thrived, based on Carnage's reaction to the Silver Surfer, former herald of Galactus. It was mistakenly believed that this was their homeworld. It is shown through the Carnage symbiote that this was a world whose dominant life forms had been overrun by the marauding symbiotes.
In Venom: Seed of Darkness #1, it is stated that when Krobaa was brought to Earth it bonded with the professor that had found him to acquire (through the symbiosis) knowledge of humanity to bring the information to a high galactic order that valued "diversity of mind above all else", but Krobaa was infected with the madness of the human mind. Attacking all living things claiming to feed on their fear (much like Dreadface) and only after Eddie Brock's camera flash had weakened him, Krobaa regained control of himself and committed suicide to save other planets from the "plague of madness."
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