Guardians are the protectors of The Vault in Borderlands and The Vault of the Sentinel in Borderlands: The Pre-Sequel. They have alien body designs, use alien weapons technology and use extremely tough shields to protect their fairly weak bodies underneath. Primarily encountered late in both games, guardians will often be found fighting against the forces of the Crimson Lance in Borderlands and alongside the Lost Legion in Borderlands: The Pre-Sequel.
The guardians are beings left on Pandora and Elpis by the Eridian race to protect important Eridian artifacts and locations. One such location is the mine underneath the Dahl Headlands, in which three guardians (one spectral and two wraiths) have been left as protectors for an Eridian Artifact. Another, more prominent locations are The Descent and Eridian Promontory where the guardians have been set up in defensive positions covering the entire approach to The Vault.
The Guardians of Elpis revealed the secrets of the Vault of Sentinel to Colonel Zarpedon and her Lost Legion, and fight alongside them to keep it a secret in Vorago Solitude, Outfall Pumping Station, Tycho's Ribs and Eleseer.
Guardians seem to be robotic in nature and are made in image of the Eridians themselves.
Shock damage is very useful for stripping away a guardian's powerful shield. Once the shield has been depleted, the guardian itself is not particularly robust and will succumb quickly to subsequent damage. Eridian weapons work just as well as shock.
The unusual pattern, speed of their movement and slender bodies can make guardians difficult to target effectively, so using an automatic weapon or a shotgun can be useful in many cases.
Their heads hang in front of their chests on long, lanky necks and are quite small, making it difficult to achieve critical hits from a distance. However, with the position of their heads, it can be quite easy to score accidental critical hits from body shots when the guardian faces towards a shooter. The region to aim for is the area where wings are connected to the body, or the upper back.
In Borderlands the Hunter talent Trespass can be the bane of the guardians once it has been advanced to its maximum level. It will allow bullets to bypass a guardian's formidable shield to apply the weapon's full force to the relatively low life of the guardian.
Guardian Types (Borderlands)
The Dahl Headlands
The Descent and Eridian Promontory
Guardian Types (Borderlands: The Pre-Sequel)
- Staff welding:
- Guardians are hostile to Crimson Lance units, and when they appear together in Crimson Enclave, The Descent and Eridian Promontory, they will fight each other. This can be used tactically by lending assistance to the weaker side, or players can alternatively watch for opportunities to snatch a kill in order to gain the substantial experience rewards.
- Guardians grant very high XP rewards in comparison to their difficulty, making them ideal to use for experience point farming.
- If the guardians that use melee attacks are unable to reach their target, they will start firing plasma bolts instead until a target becomes accessible.
- The guardians' origins were open to speculation from their first appearance in Borderlands (see talk page), but in The Holodome Onslaught DLC for Borderlands: The Pre-Sequel Athena confirmed that guardians «are biomechanical constructs ... but not flesh and blood».
- The Borderlands strategy guide mentioned Scooter's theory about guardians' origins: they're cyborg sent back from dystopian future to impregnate his mother, thus creating an offspring capable to preventing the horrible future they come from.
- Guardian types' names reference to the Christian Hierarchy of Angels (but with reversed significance):
- Sera — Seraphim
- Cheru — Cherubim
- Opha — Ophanim
- Dominant — Dominions
- Virtuous — Virtues
- Principal — Principalities
- Arch — Archangel
- Putti — Putto, which isn't an angel type but an image of child similar to Cupid in Renaissance and Baroque art.
- Guardians appear in fifth episode of Tales from the Borderlands — The Vault of the Traveler. They guard Traveler's teleportation gland and use model of Guardian from Borderlands with Cheru Guardian's staff from Borderlands: The Pre-Sequel, at the same time they act like Sera Guardians in first game.
- Famous concept artist Keith Thompson is responsible for Eridian Guardians and weapons designs.
- For Borderlands he made concept arts of Sera Guardian and Arch Guardian, but game actually use one model of second type, with one pair of wings and different attachments including Arch's back mortars. For Borderlands: The Pre-Sequel were made new models based on both concept arts but without back mortars and Sera's abdomen guns (they were replaced by guns in their hands).
- Guardians description from Thompson's official site: «Ancient alien robots left behind to administer and guard abandoned cities. Faces reform to approximately mimic the appearance of whatever species it interacts with». 
- In Borderlands guardians bleed blue blood, while in Borderlands: The Pre-Sequel, with enabled Nvidia PhysX, they bleed purple liquid similar to slag in Borderlands 2.
- In Borderlands game files were left model and animations of unused type of guardians — Cherub. It's obvious that it become a Putti in Borderlands: The Pre-Sequel.