Most of the hardcore Marvel fans know that Venom was first introduced as Spider-Man's "bio-organic" suit during Secret Wars, and was eventually revealed to be a sapient organism ("symbiote") that he eventually peeled away from because Peter disagreed with the symbiote's influence and what it was doing to him. It's only after the rejection of the symbiote by Peter Parker that it seeks a new host, and that new host is Eddie Brock.
The recent Sony movie, Venom, separated Venom from that storyline, giving him his own genesis that had nothing to do with Spider-Man. Of course it was probably a legal decision; Spider-Man is a Marvel property, owned by Sony, and on loan to Marvel Studios (hi there, Tom Holland! waves). So eliminating him from Venom's story is a wonderful solution to a host of problems.
It's also an amazing storytelling opportunity, and the Venom scriptwriters take full advantage of that fact.
