A preeminent scientist, Doctor Braun headed up many astonishing experiments in his long and varied career, but of most interest were his theories on advanced life preservation. It is said that the U.S. Army had contracted Braun to develop various methods of sustaining human life in case of an atomic war. When the war did come, Braun escaped to the safety of Vault 112 and is there to this day, his wizened and wrinkled form given new (virtual) life as a pigtailed little scamp named Betty.
Born in the town of Kronach, Bavaria, Germany, Dr. Braun was the Director for Vault-Tec's Societal Preservation Program, and notes from other Vaults suggest that he was an outside point of contact for Overseers during the Vault Experiment, either as administrative authority or expert scientific adviser. Though early correspondence showed him taking a larger role in activation and assignment of the Vaults, much of his responsibility has lapsed as he has become more immersed in, and obsessed with, the sole administration of Vault 112's Virtual Reality experiment.
For the past two centuries, Braun has been repeatedly creating and exploring new simulated worlds such as "Toucan Lagoon" and "Slalom Chalet," but often becomes bored and began manipulating the simulations to impose cruelty on the other Vault Dwellers in the simulation, as an attempt to entertain himself. A failsafe terminal in Tranquility Lane shows that Braun commissioned the "Chinese Invasion Failsafe," a means of permanently killing the inhabitants of Vault 112, but (much to his disappointment) it will not kill him, which would leave him trapped alone in the simulation.
In the current simulation world of pre-War "Tranquility Lane", Braun has taken up the identity of a little girl named "Betty" in another attempt to entertain himself - in the simulator he can be anything he wishes to be, and he happens to feel like trying out the form of a young girl. As "Betty", Braun speaks in the perfectly simulated voice of a real little girl but once he is revealed, he tends to alternate between the "Betty" voice and his real voice. Most of the residents of Tranquility Lane are unaware of Betty's nature, though a few are vaguely aware she's important and one child says "she's mean." The only person who is aware of Betty's true nature is Old Lady Dithers.
When James approached him for assistance in retrieving the one usable G.E.C.K. in the Capital Wasteland, Braun trapped him in a simulator pod.
Braun has a tremendous ego, an inflated sense of his own intelligence, and anger problems. He lashes out over perceived slights, believes that he is always right, and answers even simple questions with lengthy digressions.
Tranquility Lane: Braun (aka Betty) is the man pulling the strings when the Lone Wanderer enters the Tranquility Lane lounger. He tasks the Wanderer with all sorts of malicious objectives, the pursuit of which nets a lot of bad Karma. Activating the failsafe gives you good Karma for ending the torment of the residents in Vault 112. Doing every task of Betty's except the "Kill Everyone" task and activating the failsafe instead will result in neutral Karma.
If the player attacks Betty in the simulation, even after completing the quest, Betty will say "You can't do that here, and now you have to pay," upon which the player is killed instantly in what appears to be a pulse blast.
If you enter Braun's pod through console commands and attempt to speak to him, the game will say "Stanislaus Braun is unconscious". If you subsequently resurrect Braun, a 'normal' version of Braun will appear in or next to the pod. He will not move, cannot be killed (even with console commands, a rarity among characters in Fallout 3), and will have the standard dialogue options and voice of a male NPC.
Being born long before the Great War, Braun is one of the oldest human characters in Fallout (as the captives of Mothership Zeta are older solely due to cryogenics).
It is possible to see the sleeping body of the real Braun in a separate chamber in his office, but he cannot be damaged or disabled. Even if the player decides to run the fail-safe and permanently kill the other residents of the Vault, Braun notes that Vault-Tec failsafes prevent him from dying, perhaps forever.
Stanislaus Braun is the only person in the Tranquility Loungers that appears to be sleeping, as all the others are permanently awake.
Pinkerton stole a memory chip from Braun's terminal, claiming that it was like "stealing from a little girl".
In an interview with 1UP, Emil Pagliarulo revealed that Betty was partially inspired by the Twilight Zone episode "It's a Good Life" in which a small, willful child who was born with godlike powers annihilates the entire human race except for the adults in his small Ohio town, whom he keeps as his own personal playthings, tormenting, torturing, and killing them at will.