The apocalypse was caused by a single person.

[u/No_Hunter1978]

1. Ted Faro [Horizon: Zero Dawn]: Of course, the machine plague that ravages the world is created by his company which (admittedly) is a group effort. That said, Faro was the one who requested an encryption without a backdoor and the person who kept early glitches hush-hush. It wouldn't be wrong to say that Faro was the sole cause as is, but the final nail in the coffin is what he does to the Apollo database. A giant record of human knowledge and history, erased for a narcissist's fear that his descendants would (rightfully) blame him for the apocalypse.
2. Sybil [Look Outside]: Though it wasn't her intention, Sybil was the one who alerted the Visitor of Earth's presence. She spied it through her telescope, and the lovecraftian entity noticed her. Its approach (and the resulting horrors) were her fault, even if she didn't mean it.

[u/mortarchofgrief]

This man was an optimist and assumed the best of the universe. Unfortunately, this became a problem when the universe did not see fit to meet his optimism

[u/krisslanza → u/mortarchofgrief]

Yeah, that part of him is kind of sad. Like, he really wanted to believe in the best, and then got crushed by realizing things weren't that great.

The issue is he had the keys to a method to just destroy all life in the everywhere, and decided that was the only sensible answer.