Angel

The Guardian Angel is a mysterious and enigmatic presence watching over the Vault Hunters. It speaks with the voice of a human female and projects images of a white woman with black hair and piercing blue eyes, but it is unknown whether this is its actual appearance or merely an assumed appearance.

Details
The Guardian Angel watches over the Vault hunters via the ECHOnet once the central character receives a personal heads-up-display from a Claptrap. This connection is later revealed to be the Guardian Angel's 'eyes and ears' over the movements of the Vault hunters when the ECHOnet is shut down, and her messages at this point indicate her loss of awareness about the course of events.

The final cinematic reveals that the Guardian Angel is operating from, or through, a Hyperion Satellite in orbit around Pandora. It has been speculated that the satellite was originally tasked with the purpose of monitoring the Vault, although the person or people behind such a move are widely disputed. Whatever the case, the satellite remains almost as much an enigma as the Guardian Angel using it.

While her exact motivations are unclear, the Guardian Angel is keenly interested in the Vault hunters obtaining all of the fragments of the Vault key and being present at the Vault when it is eventually unsealed. Her reason is to prevent The Destroyer imprisoned within from escaping the confinement of the Vault. This goal is ultimately carried out by the Guardian Angel's deceit, something she expresses regret about having to do, but insists that it was the only way to ensure that events unfolded appropriately.

From hints dropped throughout the game, it can be concluded the Guardian Angel is not human. Instead, it appears that the Angel is an artificial intelligence or organic computer that is connected to the ECHOnet, through which it monitors the movements of the Vault hunters. How the Guardian Angel communicates with the central characters remains unclear, although it is notable that her first transmissions appear to be like a telepathic missive, sent directly into the mind of the character.

Additionally, the player receives two communications from the Guardian Angel regarding the window for opening the Vault by saying, "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 two-hundred years. The latter implies that the Angel's lifetime is over two-hundred years, or that, coupled with the former comment, she is not tethered by an organic life span.

Speculated origins
An in-depth list of theories can be found on the Talk Page.

Trivia

 * The Guardian Angel is portrayed by actress Britanni Deniece Johnson.
 * The following videos show her transformation to the Guardian Angel, step by step.
 * Near the start of the game where the first claptrap is to be repaired, the Guardian Angel begins a sentence with the words, "would you kindly". This has been speculated as being a Bioshock reference.
 * Hyperion, the titan of light, literally means "Watcher from above," reinforcing the notion of the Angel being connected with Hyperion. As Titans were before gods, it is possible that the company is indeed connected to the Eridians, and by extension Guardian Angel.
 * The Guardian Angel has feeling for Claptraps and the people of Pandora when they are shot, just like the Claptrap who got shot in Fyrestone at the start of the game.