One day you'll finish badly, Strelok.
One of Strelok's companions and one of the oldest legends of the Zone. Doctor, or "Doc", was said to be one of the original Stalkers to enter the Zone. It is also said that he reached the center of the Zone and even made it to the Wish Granter. He lives in the most remote of marshes and it is likely that only Strelok's group personally knew Doc. When Doc does travel, he is often accompanied by his pet Pseudodog that he tamed.
The Tale of Doctor
It is said that upon reaching the Wish Granter, he wished to have the ability to heal any living creature, even if it was beyond recovery and even dead. He was granted his wish, but he also lost the ability to distinguish mutants from normal creatures. Doc himself pretty much proves this tale is false. After meeting with Doctor in Strelok's hiding place, Doc says that nobody has ever come back from the Wish Granter alive.
One might doubt Doc's magical healing abilities, but it is confirmed that Doctor does know how to heal people using conventional methods. This is proven when he patched a dying Strelok during the events Clear Sky (partially mentioned in a conversation heard in a PDA inside Strelok's hiding place) and in Shadow of Chernobyl, where one can see a dazed and bloody Strelok storming through the door and passing out in a cut scene. Rather than reaching the Wish Granter, he (along with Ghost) find a peculiar door in the Sarcophagus, which Strelok later decrypts with a decoder made by Fang. This is depicted in S.T.A.L.K.E.R. Shadow of Chernobyl.