Vault Beasts

The Vault Beasts were creatures locked away within the Eridian Vaults, they acted as both their guardians and their captive. It was originally believed that a Vault contained infinite power, wealth or other riches and while they did indeed contain remnants of technology and even weapons, the true prize lied with power of the beasts contained within as explained by Troy and Tyreen Calypso.

Purpose of Vaults
The true purpose of the Vaults have yet to be explained by those who made them, the Eridian. However it is noted by the ancient Siren, Nyriad that the Eridian was far more intelligent than they knew what to do with, thus they sought out creatures and questions better left unanswered. This is what lead to the discovery of The Destroyer and ultimately the fall of their civilization.

It is therefore theorized that the Vaults were created to house the beings either discovered by, or created by the Eridian as a means to prevent destruction.

Known Vault Beasts
Throughout the Borderlands games the numerous Vault Hunters discover and defeat several of the beasts contained within these Vaults.

-

The Destroyer
The Destroyer is a massive, intergalactic menace being from another dimension, sealed within the Great Vault. It appears as a gargantuan, one-eyed beast with a massive mouth and several tentacles. The Eridians, at the cost of their entire civilization, imprisoned The Destroyer within the Vault thousands of years ago.

-

The Warrior
The Warrior is a biological Eridian superweapon lying dormant on Pandora. It resides within a Vault in the northern reaches of the planet, and can be controlled through the use of the Vault Key.