Dr. Knox (also spelled Nocks) is a military surgeon specializing in autopsy, especially in fire-related deaths. He first appears in chapter 36 after it appears that Colonel Roy Mustang has killed Second Lieutenant Maria Ross.
Even though he remarks to Mustang later that the burnt corpse he had received in no way resembled a woman who had died by incineration, he covers up for the Colonel and officially records the body as Ross' according to her dental records because he and Roy had been comrades during the Ishval Civil War.
Though a normal military surgeon, Knox had been one of several doctors ordered into Ishval as pathologists to gather information on the effect of burns and pain on the human body by using Ishvalans as test subjects. He became very acquainted with the Flame Alchemist's style as the expert assigned to dissect the bodies of Ishvalans that Roy had killed. Though the flashback depicts Knox as rather apathetic regarding the matter, he reveals to Dr. Tim Marcoh that he feels at odds with himself, being a doctor who kills people instead of saving them. He continued practicing pathology and forensics after the war, feeling that he had lost the right to treat living people. Even after returning from the battlefield, Knox began suffering from post-traumatic stress disorder in the form of flashbacks, insomnia, and nightmares of Ishval. He reveals to Alphonse in Chapter 57 that these visions had gotten to the point that he began thrashing around in his sleep at night. Once, his wife tried to wake him and, mistaking her for an enemy soldier, Knox tried to kill her right there in their bed. They divorced soon after that and Knox moved away from his wife and son.
Knox makes his second appearance after the mission to capture Gluttony, when Roy asks him to help treat Lan Fan's injury. Knox accompanies Mustang to the safe house where Lan Fan is being kept and operates on her, though he remarks that his skills in dealing with live humans may be rusty. While Roy, Ling and the Elrics discuss the Homunculi's possible connection to Central Command, Knox is the one who reveals to them that Selim Bradley is adopted and that the Führer doesn't have any biological children of his own. This adds evidence to the theory that King Bradley is a homunculus, as the argument that he cannot reproduce becomes valid.
After Gluttony (enraged by the sound of Mustang's name, as the Colonel had been Lust's killer) breaks free of his bonds, Dr. Knox is the one who drives the getaway car to take Roy, Lan Fan and Hawkeye to safety, continuing Lan Fan's treatment in his house.
When Alphonse brings an injured May Chang to Knox's house for treatment, the good doctor is anything but pleased, as he now has two patients taking up space in his home. The situation is not helped any by the fact that, as members of opposing Xingese clans, Lan Fan and Mei are kept from fighting each other only by way of Knox's angry intervention. As Al helps to tidy up the doctor's pig sty of a bachelor pad, Knox recounts to him the tragedies of Ishval.
In Chapter 63, immediately after May Chang and Lan Fan (fully recovered) both leave with the Elrics in tow, Knox is visited by his ex-wife and son, who reveals that he has been studying medicine in his father's footsteps. Though Knox is initially furious that his son would follow after him, knowing what he was forced to do as a doctor in Ishval, he softens up a bit when the young man tells him not to run away from his calling and professes a wish for the two to save lives together. Knox invites them both in for coffee and tearfully takes a step toward repairing his shattered life.
He is seen one last time in the final chapter, leading Dr. Marcoh to treat the blinded Mustang.
- Doctor Knox is probably a reference to the real Robert Knox since both have the same name, some physical similarities and were military surgeons specializing in autopsies and Pathologists.