[annnd ashley would be right in that guess.] Now where's the fun in that?

'Cause of what they'd found on the planet before: ruins from a hyper-advanced alien civilization. Weapon corporations reverse-engineered everything they could get their hands on, and technology advanced like crazy. Not really a stretch people started talking about what else the Eridians left behind. Urban legends get outta hand that way.

[as for the alien itself...]

We were told... [or, rather, not told until the very last minute.] The Eridians sealed that thing in the Vault so it wouldn't destroy the whole universe. It was called the Destroyer. Real points for creativity to whoever named it.