Eridian

Eridians (Pronounced 'ey-rih-dee-an' or 'air-ih-dee-an') were the aliens that created the Vault. They also created the Eridian weapons that are scattered around Pandora.

History
Little is known about the Eridians, although their importance is unquestionable. What is known is that they had advanced to a technological state far superior to that of humanity and had maintained at least part of their society on Pandora. Not only did they create the Vault, but they are also believed to be responsible for leaving the Guardians behind to protect it. It has also been determined that their entire civilization has been destroyed at some point after the creation of the Vault. Eridian ruins can be found in several locations on Pandora as a final testament to that civilization.

By reverse-engineering broken remnants of alien technology, of possibly Eridian origin, 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. Their find triggered the "gold rush" of corporations to planets like Pandora and later, the tales of the Vault.

Biology
Because of the shape of their weapons, and the design of the Guardians, it can be assumed that the Eridians were roughly humanoid in nature. By looking at the guardians of the Eridian artifact in the excavation site in the Dahl Headlands, you can assume these guardians are based on the Eridians. In that case, Eridians were tall, and rather skinny, but had very strong arms and legs. They are humanoids, so their weapons and technology were based on the fact they had two arms and two legs. Living a long time on Pandora means they must had a tough skin and a strong body to resist the dangers of the planet, and a very intelligent brain.

Society
According to Patricia Tannis the Eridians maintained a "class-based society which is capable of both leadership and organized warfare". She managed to determine this by translating Eridian writings found in Eridian ruins using her translation program as can be heard in one of her data recorders in Rust Commons West.