Angel

The Guardian Angel is a mysterious and enigmatic presence watching over the player. It speaks with the voice of a human female and projects images of a beautiful woman with black hair and piercing blue eyes, but it is unknown whether this is its actual appearance or merely projected images to appeal to the player.

The Angel watches over all of the player's actions through the ECHO-net, a satellite network for communication setup by the Dahl Corporation for communication across Pandora. The player receives an ECHO device from a Claptrap after disembarking from the bus at the beginning of the game. It seems like the Angel uses the Claptraps to guide the player through the game, since they open access to areas and the Angel is very interested in seeing them operational.

While her exact motivations are unknown, she is keenly interested in the player obtaining all of the pieces to the Vault Key and being there for the Vault's opening, which can only be done every 200 years. We do know that the Angel is not affiliated with Atlas or the Crimson Lance, since she opposed them throughout the game.



Speculation
From clues and hints dropped throughout the game, it seems like the Guardian Angel is not human, at least not anymore. Instead, it seems like the Angel is an AI that is either plugged into Dahl's ECHO-net or actually onboard the satellites that manage and transmit the ECHO-net, through which it monitors and communicates with the player. However, this is unlikely as you get a transmission from her before receiving an ECHO.

Additionally, the player receives two communications from the Guardian Angel regarding the window for opening the vault by saying that "We will not have another opportunity to open the Vault in this lifetime" and "We will not have another opportunity to open the Vault in your lifetime," referring to the Vault only being able to be opened every 200 years.

Since opening the Vault releases The Destroyer, it can be assumed that either the Vault is a prison for the terrible monster or a gateway it is using to try to enter this dimension. Either way, it seems that the Angel's purpose in guiding the player to the Vault is to prevent The Destroyer from entering this world by defeating it.

Here, a picture of the Satellite that is the supposed to be Guardian Angel or a tool of hers.

Perhaps the satellite serves as a 'host' for the Guardian Angel, much like The Destroyer which apparently also needs a host to exist on a particular dimension/plane.

Possible origins:

From various clues in the game, It may be concluded that the Guardian Angel could be either an AI created by Tannis either for company in her psycosis, or acccidentally created when her computers were fried while she was trying to transilate Eridian writings. Another possibility is that the Guardian Angel is a split personality of Tannis, which expressed it's self thorough the ECHO network.

Clues that lead to this are as follows:


 * Tannis "pratically invented" the ECHO network which The Guardian Angel relies on.
 * Tannis called the ECHO recorder "Two timing" suggesting there was another being in her encampment, Even though she was the only living human there.
 * Tannis says "Did you get my message?" When you discover her in a cell. And "they were foolish letting me keep my Communicateor" meaning that her alter-ego could have sent the message from the cell.
 * The paper you get from her is written in the form of an argument with an "invisible cellmate". Could be The Guardian Angel.
 * The connection explains how The Guardian Angel has such knowledge of the vault. Since it could be either a split personality of Tannis or an A.I. made from Tannis's attempts to transilate Eridian writings. The Eridian's may have "Written in" an AI to act as a safeguard.