American serial killer (1858?-1896). Born Herman Webster Mudgett in Gilmanton, New Hampshire. He attended medical school in Vermont and at the University of Michigan, where he seemed to specialize in dissection. He was expelled for stealing corpses for insurance fraud schemes. He then traveled across the Midwest running cons and marrying an unknown number of women for their money.
In 1886, he took the name "Harry Howard Holmes" and using his medical training, got a job in a Chicago drugstore owned by Mrs. E.S. Holden. He was able to turn the store into a success and was able to take Ms. Holden as his lover. Soon enough, Ms. Holden became the late Ms. Holden, and Holmes used the proceeds from her store, her life insurance policy, and the sale of her skeleton to a medical school to begin building himself a mansion.
A crew of 800 workers under Holmes' direct supervision labored from 1888 to 1890 building a three-story mansion/storefront/office/apartment complex at 701-703 West 63rd Street. In addition to turrets and battlements, the 105-room mansion also featured hidden gas jets in the guest rooms, an elevator shaft with no elevator, stairs to nowhere, peepholes, secret alarm bells activated by opening apartment doors, hidden passages, soundproof asbestos-lined vaults, kilns, quicklime pits, trap doors, chemical labs, a glass-bending furnace, and a nine-room basement illegally hooked up to the city's gas mains.
When the "Murder Castle" was completed, Holmes went about killing his secretaries, office girls, wives, at least 50 paying guests, and many others. He dissected the bodies, performed chemical experiments on them, and saved some pieces in his vaults. He disposed of most of the evidence in his quicklime pits or in the furnace (including -- irony of ironies -- Wade Warner, the furnace designer).
Of course, running a Murder Castle is expensive, and Holmes, though an excellent murderer, was no damn good at raising money. Holmes burned the third floor of the mansion for the insurance without realizing that the insurance adjuster would want to see the damage. He tried to marry Minnie Williams, a wealthy Texas heiress, but her sister objected, and Holmes ended up killing both of them--too bad the Texas courts refused to transfer their property to him without death certificates. He talked a dimwitted sidekick, Benjamin Pitezel, into faking his death for money, but Pitezel ended up dying for real, and Holmes killed Pitezel's children trying to claim the money. Holmes was arrested, and the Chicago Police broke into the Murder Castle and discovered what Holmes had been up to.
Holmes was convicted of only Pitezel's murder and was never charged with any other deaths (Chicago police estimated that he had killed 50 people -- most scholars believe that count is woefully inaccurate, and some place the death count at over 200...). Holmes was hanged on May 7, 1896. The Murder Castle burned to the ground on August 19, 1894 before a complete search of the property could be made.
(While researching this, I stumbled onto a business called "H.H. Holmes Testing Laboratories" in Wheeling, Illinois, a Chicago suburb. Though the H.H. Holmes at the testing lab isn't the same guy as the serial killer, you'd think someone from the Chicago area would know better than to name a business after a homicidal maniac...)
Primary research: Suppressed Transmission: The Second Broadcast by Kenneth Hite, "The Extra 'H' Is for 'Homicidal': H.H. Holmes", pp. 74-77.