Commandant Steele

Background
Commandant Steele is the leader of the Crimson Lance forces on Pandora. It has also been speculated that she might be a Siren, a possibility hinted at by her tattoos and the demonstration of her ability to form the vault key fragments together.

Involvement
Commandant Steele is the main antagonist in Borderlands. She leads the Crimson Lance army, the lawless fighters encountered in Old Haven and beyond. She claims the Alien Technology she believes to be hidden in the Vault as the property of Atlas corporation and tries to take the vault keys by force after the last piece is collected.

The first time that she is seen is shortly after Sledge has been killed and the first Vault key piece has been acquired. At this point she transmits a message commanding that the vault key piece be turned over to the Crimson Lance, although the message is ultimately ignored and the adventure continues. It is also possible to receive a transmission en route to Sledge's Safehouse, where Steele berates the Vault hunters for accepting a mission to assassinate a "local leader".

Her later machinations involve impeding the progress of the Vault hunters, both by sending her forces to attack (in the hope of taking the vault key fragments) and by commandeering the ECHOnet. Just before the ECHOnet gets shut down it becomes clear that she is making a stronger bid for power than originally expected when Crimson Lance forces under her control are reported to be assaulting Sanctuary. Shortly thereafter she is briefly seen ordering Master McCloud to execute the Vault hunters.

When she is eventually encountered in person, the meeting is cut short; During the cut-scene, she announces that the Vault and its riches are the property of the Atlas Corporation and that the Vault hunters belong to her. After connecting the Vault key fragments together and placing them in the keyhole, pieces of the surrounding ruins merge to form a portal to the Vault. Steele is under the belief she has won and begins to celebrate when a tentacle pierces her from behind and drags her into the mouth of a huge beast known only as the Destroyer.

Quotes
Notes:
 * "This is Commander Steele of the Atlas Corporation Crimson Lance, D Company, 3rd Starborne Brigade. I've just been informed that you have arrived on Pandora in search of the Vault, and within minutes, have started killing the locals and causing a disturbance. This planet is under the authority of the Atlas Corporation, and any Eridian artifacts found here are Atlas property; possession of such property carries a stiff penalty. I invite you to turn yourself in at once to the near Lance outpost and surrender any information or artifacts in your possession. Consider this your one and only warning." - upon completing Sledge: Battle For The Badlands
 * "It's come to our attention that you've been at war with elements of the local population, and you've now been contracted to assassinate one of their leaders. This type of unsanctioned mercenary activity undermines the stability of the region. You have been warned! These continued insurgent activities will not be tolerated. Abandon this futile pursuit, and turn yourself in while you still can." - may arrive while in the Arid Hills
 * "Listen up, merc. There is no fourth key fragment. Tannis has joined us, and we now have possession of the completed key. She used you to get what she wanted. You've ignored my orders, but I'll cut you a deal, leave the planet now, and we won't pursue you. Do yourself a favor, take advantage of my generosity while you still can. Any further disobedience will cost you and the citizens of this planet dearly."
 * "This is Commander Steele of the Atlas Corporation Crimson Lance, Starborne Brigade. Be advised. In preparation of upcoming special operations of the Lance, I have ordered the ECHO network shut down. Any attempt to circumvent our control will be met with punishment of death. Do not test me, or we may shut down the commerce grid as well. This is the only warning you will receive."
 * "YOU WILL BE... DESTROYED!!!" - upon entering the boss area of The Backdoor
 * "DEATH TO ALL/ANY WHO OPPOSE US!" - upon entering the boss area of The Backdoor, alternate quote
 * "You have failed to listen to Commander Steele. I've warned you time and again, yet you persist on ignoring my orders. The contents of the Vault are rightfully the property of the Atlas Corporation. But you? You belong to me." - cutscene at the Vault
 * "Yes, the key works. Sergeant, get your team ready to go inside. It's time to claim what's rightfully ours. As for this, Tannis could use some company in the brig... We'll deal with that problem later." - cutscene at the Vault, Steele's last words
 * The sub-titles refer to her as "Commander" rather than "Commandant".
 * Her last quote is supposed to be cut by her being impaled by the Destroyer after the word "inside". The complete quote is shown when subtitles are enabled.

Trivia

 * Though never mentioned in game, a string that was ultimately dropped from the final release lists her given name as "Helga".
 * She bears similar tattoos as Lilith and might be the Siren she is looking for.
 * She also bears an uncanny similarity to the original design of Lilith when the game was announced to GameInformer.
 * Despite being killed by the Destroyer, if Master McCloud is fought again later, she will be there yelling "Death to all who oppose us". She also performs the same animation she does when she places the key in the Vault, right before she gets stabbed.
 * Tannis once referred to her as an "albino" due to her extremely white skin. This reference is made again by General Knoxx.
 * General Knoxx dislikes Steele because "she talks too much". Knoxx states this dislike right after accepting You've Got Moxxi: Moxxi's Red Light and thanks the Vault hunters for turning her into a "meat kebab".
 * Knoxx also calls Steele bulimic in the 5th ECHO recording of the Knoxxed Out mission.
 * When she activates the Vault Key, her hand produces blue mist not unlike Lilith, adding to the speculation that she is a siren.
 * Originally, it was possible to see what Steele would have finished saying in the Vault if she hadn't been interrupted by the Destroyer by watching the cutscene with subtitles enabled. It seems that she was planning to throw the Vault Hunters into Tannis' jail cell to keep her company. This has since been partially fixed, though the subtitles do still show a little of what she says after she is killed (as opposed to being cut off midway).
 * Moments before getting killed by the Destroyer she says "Yes, the key works. Soldier, get your team ready to go inside" but the subtitles show Sergeant instead of Soldier, however, when you first encounter her in the 4th DLC, the subtitles show Soldier.