|“||All here, Colonel, all here! We are the government you people deserve!||„|
— The Doctor to Miller, replying to his question of where the Government is.
The Doctor was originally, just as his name implies, a doctor in the Yamantau Bunker during its construction. He became trapped in the bunker when the bombs fell, with around a thousand other survivors. These were mostly workers and some communications officers. The group ran out of food and were forced to resort to cannibalism. It was presumably the Doctor's idea to use the recently repaired antennas to lure other survivors to the bunker, so the Cannibals could eat them. In any case, by 2035, the Doctor emerged as the leader of the group, being one of the few men in the bunker to have retained his higher brain functions and any sapience.
The Doctor is first heard shortly after the Aurora and it's crew escape from Moscow, in a repeating radio signal urging survivors to regroup at the Yamantau bunker as part of the "Ark restoration project". The Doctor later contacts Miller directly over the radio and poses as a government official following the Aurora's crossing of the Volga.
When the crew get there, Miller, Anna, and Artyom are led to a room with a glass separating them from the "ministers". They realize too late that something is wrong, as they are soon swamped by dozens of Cannibals and knocked out. When they wake up, the Doctor greets them and reveals the sinister truth about the bunker. He takes Anna away to be tested for diseases (due to her cough), while threatening Artyom and Miller to call the rest of their crew, if they don't want Anna to be tortured. He leaves shortly before Artyom and Miller are rescued by the Rangers. When Artyom frees Anna, the Doctor knocks him down with a metal rebar, only to find himself held at knifepoint by Anna. He desperately begs for his life, but to no avail, with Anna silting his throat moments later.
Anna later reveals that the Doctor discovered her lungs were falling apart (due to the poison gas she inhaled) when he examined her, but she kept it a secret, not wanting to worry anyone.