Eridian

The Eridians (Pronounced 'ehr-i-den') are the aliens that created the Vault. Little is known about this race, though their importance is unquestionable. By reverse-engineering broken remnants of their technology, humanity made centuries of technological advances almost overnight. It also made the Atlas Corporation the most powerful company in human space as they were the original discoverers; this find triggered the "gold rush" of planets like Pandora as well.

Artifacts & Presence on Pandora
Eridian technology seems to be at least somewhat biological in nature; most artifacts tend to have a flowing, organic appearance. Their weapons are some of the rarest of the rare. They fire blasts of energy and have unlimited ammunition with no need to reload. After they run out of energy, they simply need time to recharge. They are made out of a much heavier material than normal guns.

Many believe in a mysterious Vault, said to have been built by this ancient race and filled with their advanced technology...

Guardians
The Guardians are beings left on Pandora by the Eridian race to protect important artifacts and locations; one such location is the Vault. They seem robotic in nature, though they have many organic parts and bleed blue blood. They have an alien physiology, use alien weapons, and use extremely tough shields to protect their weak bodies. It is unknown if they are Eridians chosen to guard their valuables, or created by them for that same purpose. There are many varities of Guardians, some with the ability to fly.

Behind the scenes

 * There are references to the Christian Hierarchy of Angels with the enemies guarding the vault: Sera Guardians - short for seraphim, Arch Guardians - short for archangels, and Principal Guardians - short for Principalities.

Appearances

 * Borderlands