Borderlands is set on the planet of Pandora. Lured by its apparent vast deposits of minerals, several colonization ships sponsored by the Dahl Corporation (one of several diversified mega-corporations that appear to control and govern entire planets) journey to the planet and build settlements there. The mining operations are cost-effectively manned by large amounts of convict labor brought to the planet by Dahl.
Prior to the events of the game, one of the other mega-corporations, known as the Atlas Corporation, had found an ancient vault on a nearby planet known as Prometheus, filled with alien technology that allowed them to make leaps and bounds in starship and weaponry technology, and overtake their competitors. The presence of similar alien ruins scattered across Pandora spurs the Dahl Corporation to undertake an extensive search for a possible vault on Pandora, headed by a respected xeno-archeologist by the name of Tannis. However, the Dahl-sponsored search for a vault on Pandora turns out to be fruitless, and the massive industrial mining operations soon deplete the bulk of the mineral deposits. Furthermore, the coming of the planet's summer unleashes hordes of dangerous alien wildlife coming out of hibernation.
Those who are rich and important enough to do so leave the planet, leaving the rest of the population to scavenge for their living in isolated settlements, seeking out a living in the barren wastelands and industrial trash heaps across the planet. To make matters worse, the Dahl Corporation simply opened the gates of the prison labor camps during their departure, and gangs of bandits terrorize the populace. Despite the lack of evidence of its existence, legends persist of "The Vault"—a supposed treasure trove of alien artifacts, technology, and of immeasurable wealth—but it is rumored that any who had discovered it were wiped out by a protective force, leaving few clues as to its location or purpose while a myth was born of the marvelous treasures within.
Borderlands begins some time after the Dahl Corporation's abandonment of Pandora; several fortune seekers, including the player, are drawn to the planet by its legends of an unopened Eridian Vault. After arriving at the town of Fyrestone, the player sees an image of a mysterious woman, the "Guardian Angel", who is aware they are here to seek the Vault and directs them to follow her instructions. The player meets a man named Dr. Zed and the doctor helps the player through the beginning of the game. The Angel eventually leads them to collecting one of the several artifacts needed to open the vault. This causes Patricia Tannis, an archaeologist/scientist, to contact the player and urge them to collect the other three pieces of the Vault key. Tannis reveals that the Vault opens every 200 years and the time of the next opening is approaching. At the same time, Commandant Steele of the Crimson Lance, a well-outfitted mercenary force in the employ of one of the game's several mega-corporations, threatens to declare martial law over the planet and demands the vault key pieces.
While the player is able to secure the second and third Vault key pieces without incident, they find that the final piece is not where it is expected. Steele contacts the player, revealing that Tannis had betrayed them and that there are in fact only three pieces, then proceeds to cut off the planet's ECHO network disabling further communication with the Guardian Angel. The player infiltrates the Crimson Lance's headquarters and finds Tannis locked up; she claims she had no choice but to betray the player under force, but urges the player(s) to restart the ECHO network and to prevent Steele and the Crimson Lance from using the key. After restoring the network, the Guardian Angel urges the player to hurry and stop Steele. The player finds, as they approach the Vault, that the Crimson Lance are in combat with alien Guardians; after bypassing both forces, the player finally arrives at the Vault, too late to stop Steele from using the key. However, when the Vault opens, Steele and her guard are wiped out by a giant monster that is attempting to escape the vault. The Guardian Angel explains that the monster is called the Destroyer, imprisoned in the Vault by the alien Eridians long ago to prevent it from destroying the universe, with the Guardians present to prevent anyone from opening it. The player is able to defeat the monster, sealing the Vault for another 200 years. It is revealed that the Claptrap from the beginning of the story is really an Interplanetary Ninja Assassin Claptrap made by Hyperion. The player is also shown that the Guardian Angel is a Hyperion satellite orbiting around Pandora communicating with the player through the ECHOnet.
There are four playable characters in the game; though each is given the character's official name by default, the player may change their character name or the colors of various parts of their outfits at "New-U" stations throughout the game. Brick is a Berserker, a tank-style character who is strong in melee combat. Bricks' preferred weapons are explosives and rocket launchers. Brick has the special ability to temporarily enter a berserker rage mode during which he cannot wield guns, instead using his massive fists to rapidly pound his enemies to death, and rapidly regenerates health and is resistant to damage during the rage. Besides being a melee expert, Brick can use explosive damage more efficiently than the other classes. Lilith is one of only six known Sirens in the galaxy, beings with superhuman powers but with no way of controlling them. Lilith's Phasewalk ability allows her to temporarily enter another dimension, which renders her invisible to enemies, makes her move faster and she is unable to take damage from enemies (and only give damage when exiting Phasewalk). Her Phasewalk causes a powerful shock-wave blast that can damage nearby enemies whenever she enters and exits Phasewalk. Liliths' preferred guns are elemental tech weapons and some of her skills focus on improving her "damage over time" with elements. Mordecai, a Hunter, specializes in using Sniper Rifles and Revolvers and is aided by his pet Bat-like bird, Bloodwing, which can be used to assist in his long-range attack skills and scavenging for loot. Roland, a former member of the Atlas Corporation's private Crimson Lance army, is described by the game as a "Soldier" and is able to deploy an automated gun turret that can be upgraded with a wide range of offensive and defensive abilities. Roland is a good freewheeler and prefers shotguns and combat rifles. Accompanying the standard weapons, all characters also have a melee attack.
For the most comprehensive Borderlands information on the internet head over to the Borderlands wiki. But there will eventually be alot of BL info here:)