Doctor Holmes in the popular imagination refers to the individual who called himself "H.H.Holmes" in the Chicago of the 1890s. This was almost certainly an alias. Holmes was the first well-known serial killer in America, murdering perhaps dozens of people (although it could have been far fewer or far more).
The site of his crimes was a building he constructed in 1893. Known as "The Castle" by locals, its ground floor housed a pharmacy operated by Holmes and the upper floors were ostensively a hotel. In fact, Holmes had constantly replaced his builders and contractors during construction. According to then-current law, this helped him avoid paying them. It also kept anyone but Holmes himself knowing the details of what newspapers later dubbed his "Castle of Horrors." Windowless rooms, maze-like hallways, secret passages, lime pits, even an ersatz gas chamber made up the secret part of his three-story home/office. Some hotel rooms were designed to seal themselves completely then receive gas. A peephole allowed Holmes to watch his victims die. Dark hallways were sometimes used to "hunt" young women.
In the basement were lime pits, two large furnaces and a dissection room. Holmes was known to have sold his victims' skeletons to medical schools. Unlike the majority of serial killers, he managed to make a profit from his crimes, but the sadistic and ritualistic nature of the murders make him more than simply a killer-for-profit.
With his creditors closing in upon him, Holmes vanished in 1895. Within the year, officials seizing his property for unpaid bills discovered human remains in The Castle. Further investigation sparked massive publicity and a manhunt that went on for decades. Rumors of his appearance were wide-spread, often contradictory, and continued even during the Second Great War. But Holmes himself was never found.
Most historians believe Holmes was in fact Herman Webster Mudgett (born 1860) a New Hampshire native who was a bigamist and con man.
Doctor Holmes became a stock character in melodrama--the cruel genius with elaborate traps with which to murder the innocent. Two common facets of the fictional Holmes was an assumption that he might have found a means of attaining immortality by extracting life (or something) from his victims, and the identification of him with the English serial killer Jack the Ripper, who also remained uncaught.
Some conspiracy theorists maintain Holmes was the alternate identity of Tomos Armstrong Kuster. Serious historians point out this is impossible according to the records of the time, but that did not prevent comic artist Aaron Moore from making this theory the central plot point of his graphic novel Devil Doctor in Kuster has an illegitimate brother who turns out to have been Jack the Ripper, but who later kills a man named Elbert Fish, assuming his identity (in real life, Elbert Fish was a masochistic pedophile and cannibal executed by Castreleon New in 1936 at age 66).
Arguably the first fictional version of Holmes was Juliette Verne in her last novel Ligue des Étrangers, a villain known merely as "The Doctor."
Some critics (none of them French-speaking) see Baphomex as inspired by Holmes, but this is a far-from-mainstream opinion.
On the other hand, the author Henry Sarsfield Ward made no attempt to disguise the fact that his fictional villain, the diabolical Sax Romaine was inspired at least partially by the story of Holmes.