Inhabitants of Elpis typically speak with a very thick Australian accent.
Some time in the past, the Eridians built an underground complex to protect one of their Vaults. They also left Guardians as further insurance that the Vault would remain protected from those who might exploit it.
A long time later, Dahl constructed a mining colony on Elpis to tap the vast quantities of liquid methane found there. Concordia was their spaceport, and primary port of call between the moon and Pandora far below. They also established a dig site at Vorago Solitude, which at some point led to the discovery of the ancient Eridian ruins beneath.
A Dahl force, under the command of Colonel Zarpedon, also came to this site and encountered remnants of the ancient Eridians themselves. Zarpedon took steps into the unknown in dealing with the aliens, and returned to her legion a changed woman. She charged them with a new mission to protect the Vault, and in renouncing their ties to Dahl they became the Lost Legion.
Dahl's mining efforts eventually caused an event known as "The Crackening" when the moon's surface began to crack and split open. Many lives were lost as Dahl ships fell from the sky and rivers of lava poured from the cracks. Scavengers, who later became referred to as "scavs", began raiding Dahl wrecks and facilities as other survivors retreated to the last safe place on Elpis, the city of Concordia. A few years after the Crackening, the First Fleet arrived, bringing new colonists and scavengers to Elpis.
Hyperion later took a stronger interest in Pandora than they previously had when a Vault was uncovered on the world. Acting under the direction of a technician named Jack, they set up the Helios space station to exert control. Unknown to the Hyperion CEO Mr. Tassiter, Jack intended to open the Vault on Elpis, and had hired a team of new Vault Hunters to assist in this mission, sending each an ECHO invitation to come to the space station being built above Pandora.
The Lost Legion, reacting to the apparent drive toward the Elpis Vault, attacked Helios, killing hundreds of workers in the process. After taking over the station they began using the Eye of Helios, a giant laser able to destroy a large settlement, to blast the lunar core in an effort to prevent the Vault from being opened. While trapped on the station, Jack requested the aid of his Vault Hunters in reclaiming Helios and saving Elpis.