Doctor Klein is a pre-War doctor and the chief/head researcher of logistical operations and ideology at Big MT. Sometime after the Great War, he became a think tank to continue his work at Big MT. He seems to be overconfident in his intelligence, as he shows absolutely no grasp of the purpose or function of the advanced technology he tasks the Courier to retrieve.
Along with his original name and human memories, Klein has lost much of his knowledge of human anatomy, and refers to the Courier's fingers and toes as "penises". He is shown to fear and hate Dr. Mobius, although they were partners at one time. He seems to hold his colleagues in low regard, often ignoring their advice. At the end of Old World Blues, it is revealed that he and the think-tank stole the Courier's brain in order to escape their imprisonment in Big MT and go into the Mojave to conduct ruthless experiments on both the Wasteland and its denizens, much like the implementation of the Cloud in the Sierra Madre to test the chemical, Hazmat suits and Auto-Doc technology.
Sonic Emitter Upgrade: Klein wants the player character to go to the X-8 research center and take the Basic Institutional Test, which eventually leads to upgrading the sonic emitter and thus taking down the force fields.
When Dr. Mobius comments on what the scientists have forgotten, friendship is probably aimed at Dr. Klein, who barely acknowledges his colleagues, and even regards them more as understudies or employees than his friends.
Throughout Old World Blues, he speaks in a very loud voice, as apparently the other scientists or Elijah have messed around with the volume control on his chassis; this is why Dr. Klein's dialogue is always in all-caps.
Klein has a hatred for the words "mutiny" and "jism".
Inside Klein's house, directly above the door, is a large Old World flag. This could imply Klein was or still is an American patriot. This could explain his willingness to help Ulysses.
His name is a reference to the mathematician Felix Klein who thought of the Klein bottle, a three dimensional non-orientable object in four dimensional space, an equivalent to the Mobius strip in a higher dimension.
The three perks that he can give the courier (Heartless, Brainless, and Spineless) are references to The Wizard of Oz: the scarecrow was missing a brain, the tin man was missing a heart, and the lion was missing courage.