Born as Herman Webster Mudget and later as H. H. Holmes after changing his name, was the first known serial killer in American history.
Holmes also went down in history as America's first known serial killer. He was a doctor by trade who often dealt in a number of shady businesses. One of these ventures was a cure for alcoholism and a machine that could produce steam from water. After he had conned numerous people out of enough money, he opened his 'murder Castle' for the 'world county fair' where he secretly began his killing spree.
Holmes built secret torture chambers within the Hotel walls where he killed numerous victims, particularly women. The authorities began to suspect something was wrong when they found a forged certificate belonging to Holmes. He was captured and tried in a court, where he was exposed as a fraudster and a murderer. Though his killing count is estimated between 250, he confessed only to 27 murders, though the count is likely to be estimated over 100.
Holmes was eventually hanged in the late 1800s. His spirit haunts the apartments next to where he was executed. Sam and Dean also realize that Holmes is not an easy ghost to get rid of because he requested to be buried in concrete so that no one could desecrate his corpse (as he did his victims'). This wish was granted. Every ten years he would kidnap two or three girls and bring them down where he tortured them to death. He kidnapped Jo in the same manner, however she was saved by Sam and Dean. He was defeated after Sam and Dean managed to lure and trap him in a small room directly beneath an empty lot. They added a ring of salt and then closed all the exits in concrete, trapping him as he was unable to ever escape.
- Ectoplasm Secretion - Holmes could create Ectoplasm, a rare ghost power that only the most angry ghosts could create. In most cases they can create small amounts, while he was strong enough to create liters of the black slime.
- Super strength - Easily stronger than humans, he casually overpowered them.
- Teleportation - He could teleport from place to place.
- Electronic manipulation - Caused lights to flicker.