Doc Henry was always a hard one to figure out. It didn't seem to matter whether he was working with humans or dogs. He had an equal lack of affection for both; a regular Diogenes. I'm not sure what the man was after.
Doctor Henry used to work with the Enclave cyber-genetic research program at the Poseidon oil rig and at various other Enclave installations. In NCR, Dr. Henry claims he left because he felt his "work wasn't being appreciated," which is true: his theories on correcting the mutation in the Wasteland population were not popular with the rest of the Enclave scientists, most notably one of his colleagues, Dr. Schreber, who he worked with jointly on many genetic research projects in the past. Dr. Henry was arguing with Schreber at the Navarro base about the mutation problem for the five billionth time when Schreber, in a fit of anger, told Henry he was going to recommend that Henry be transferred to another Enclave facility where he would be put to work on cybernetic maintenance (the equivalent of cybernetic janitorial duty). Henry took the threat very seriously, and within hours, Dr. Henry stole a cybernetic dog (cyberdog) and slipped away from the Navarro facility, heading east and eventually making his way to NCR. The Enclave, while not pleased with his attitude and the directions of his research, were not happy with his escape (they need all the scientists they can get), and several soldiers were punished for negligence. Schreber never confessed to his role in Henry's disappearance, and simply claimed that Dr. Henry had been acting suspicious for some time, and was displaying "sympathies for the mainland mutants."
After deserting the Enclave base at Navarro, Henry successfully integrated into the NCR and runs a clinic in New California Republic. This clinic, in which he is perpetually busy, can be found directly to the south of Duppo's shop, but it is unmarked. His reason for this departure is unclear, but he hints that it was due to his "single-minded colleagues" only striving for purification. His field of expertise is cyber-genetics and he is attempting to translate this knowledge into an experimental treatment or cure for FEV mutations. The local crime lord, Merk, took an interest in his research and will hire the Chosen One to obtain his research papers.
K-9 was left in NCR by the Chosen One so that he could receive necessary repairs from Dorothy and, not long after his recovery, Dr. Henry (who had been placed in critical condition after being reportedly assaulted by the Chosen One some time earlier). Dr. Henry, afraid that too much information about the Enclave would be obtained from K-9, attempted to destroy the cyborg, but was stopped by cyberdog and Dorothy, who suspected what Dr. Henry was planning. The NCR government used the attack as an excuse to confiscate K-9 and cyberdog in order to learn more information about the Enclave as well as what makes the two of them "tick." At last report (and over Dorothy's objections), K-9 and cyberdog were disassembled and analyzed. Structural damage during the disassembling is reported to have killed them both.
Sometime after the NCR captured Navarro, he met his old squadmates, Daisy Whitman, and young Arcade Gannon along with his mother. After the NCR began hunting Enclave personnel who were attempting to integrate themselves into the NCR, they left for the Mojave Wasteland.
Despite the fact that ex-Enclave personnel (and even the children there-of) are hunted by the NCR and many others for war crimes, Doc Henry will freely mention he was a member of the Enclave while speaking to the Courier in his lab at Jacobstown. (Even before the start of the quest For Auld Lang Syne.)
If Calamity is dead he will "still hand over control of the lab to her".
"This guy is so out of place it's painful. He's got that egghead, not living in the real world air about him, that's for sure." – Fallout 2 in-game description
"Doc Henry was always a hard one to figure out. It didn't seem to matter whether he was working with humans or dogs. He had an equal lack of affection for both; a regular Diogenes. I'm not sure what the man was after." – Arcade Gannon's opinion
xbox360 Sometimes he will not perform medical services for the player. [verified]
pc Sometimes he may just say, "Keep your head down - there could be snipers around". This makes any communication with him impossible. There is no known fix for this bug, however it may work to disable, enable, kill and resurrect him using console commands. [verified]
xbox360ps3pc There may be two Henry(s) in the Second Battle of Hoover Dam, one with wasteland doctor fatigues, and one with an Enclave scientist outfit. [verified]