SPOILERS!Below is information that may adversely affect the reader's enjoyment of the game.
Angel is the daughter of Hyperion programmer Handsome Jack. The identity of her mother remains unknown, but her absence from Angel's life is a result of Angel's Siren powers killing her. Jack tethered his daughter to an interface, granting her control over most technology. He then orchestrated the events of Borderlands through his daughter.
Angel watches over the Vault hunters via the ECHOnet. This connection is later revealed to be Angel's 'eyes and ears' monitoring 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 Angel is operating from, or through, a Hyperion Satellite in orbit around Pandora.
While her ulterior motivations are unclear, Angel is primarily 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. Later in the story, it becomes clear that she wished to prevent The Destroyer, imprisoned within, from escaping the confinement of the Vault. This goal is ultimately carried out by Angel's (and, by proxy, Hyperion's) deceit, something she expresses regret about having to do, but insists that it was the only way to ensure that events unfolded appropriately. This turns out to be a lie as well, as the ultimate goal for the Vault's opening was the supply of Eridium that Handsome Jack wished to exploit for his own gain.
With a steady supply of Eridium and the Vault key stolen from Patricia Tannis, Angel's father used her as a catalyst to charge it, so he can awaken the Warrior. However, this leaves Angel dependent on a constant supply of the element, as disconnecting her from that supply will kill her.
She assists the new Vault Hunters in stopping Handsome Jack, similarly to her role in Borderlands. It is also revealed that Angel betrayed the first Vault Hunters at some point, nearly resulting in their deaths during an attack on New Haven. She betrays the new Vault Hunters as well, deactivating Sanctuary's shields, and rendering the city vulnerable to Hyperion mortar strikes, which almost demolishes the city. After said events, however, she expresses regret for doing so, and turns on Handsome Jack, and continues to assist the Vault Hunters.
She later reveals that the Vault Key is with her, but there are three obstacles between her and the Vault Hunters. The first is a 'Death Wall' that only Hyperion robots can pass, the second is a heavily armed bunker, and a door that only Handsome Jack himself may open. She suggests going to Opportunity, a massive city Jack is building, to kill one of Jack's body doubles to obtain a biosignature, as well as a voice modulator. Jack discovers her deceit, and tells her to "say goodbye." She replies with, "See you soon." Roland and a hastily recruited group of bandits led by Brick then assist the Vault Hunters in reaching Angel with an all-out assault on Handsome Jack's tower.
Once the Vault Hunters pass the three obstacles, she reveals her true form as a Siren, and her involvement in Jack's plan. She asks the Vault Hunters to destroy the Eridium Injectors. However, destroying the Injectors would result in Angel's death. She accepts this, saying it's "ending a life of servitude." Once the final injector is destroyed, Angel falls to the ground. Jack pleads with her, saying, "It's not too late to make things right." Angel, with her dying breath, calls her father an asshole.
When Tina involved Angel as an enemy in Assault on Dragon Keep, Lilith tried to explain that Angel wasn't a bad person, suggesting that Lilith may have forgiven Angel for her role in the course of events that led to Roland's death.
In Borderlands 3, Angel's powers (Phaseshifting) is definitively clarified to be technopathy, or the ability to interface with and control technology.
Angel's powers ended up manifesting themselves in Patricia Tannis, who uses them to great effect when the Vault Hunters attempt to rescue her from Pain and Terror inside Carnivora. It revealed later in a sidequest that Tannis set about recovering objects that played a part in Angel's childhood in the time between Borderlands 2 and 3, which the player can then interact with as part of the sidequest to learn about Angel's childhood (and fix a broken water purifier on the side). These objects were imbued with memories of milestones in Angel's life, such as when Jack first became aware of her powers, and when they caused the death of her mother. Other than that, her death and that of her father will likely make this the final time the two will appear in the series.
- The final cutscene of Borderlands shows a satellite orbiting Pandora with the weapon manufacturer Hyperion printed on it as well as The Guardian Angel's face. In the final cutscene, the following serial number can be seen printed on the side of the satellite: 4N631 - The word "Angel" in 1337speak. The logo of the Vault, surrounded by what look like wings, is also printed on the satellite.
- Angel is watching over the Vault hunters by way of an orbiting Hyperion satellite. The name "Hyperion" means "Watcher from Above". This satellite is later recovered by Tannis, and now rests in a laboratory below an abandoned Dahl mining facility.
- Angel appears in the Borderlands 2 artbook as "Angel". The page includes mostly concept art and what appears to be an in game model. The concept art shows her with the tattoos of a Siren.
- At the beginning of Borderlands 2, while Angel is hacking a door she says "executing phaseshift." Since Siren abilities are known as "Phase-" (Lilith's Phasewalk and Maya's Phaselock), this appears to be what she calls her Siren power.
- In the concept art book that came with the Collector's Edition of Borderlands 2, it is stated that Brittani Johnson was cast as the Guardian Angel before the character was designed, which lead the designers to base the CG version off her real appearance.
- An allegory of Angel appears in Tiny Tina's Assault on Dragon Keep in the form of an NPC called the Sorcerer's Daughter.
- In Borderlands: The Pre-Sequel, Angel appears in a picture frame on Jack's desk.