Haunter is a purple Pokémon with a gaseous body. It has a round head with a pair of disembodied hands. Each hand has three pointed fingers. Its head is flanked by three large, spiked protrusions on either side, and its eyes are large and triangular with small pupils. The gases composing its head curve down to form several pointed teeth framing a pink mouth and a long tongue. Its body tapers into a jagged tail.
Haunter hides in very dark places, where it plots to take the life of the next living thing that comes near it. If a human or a Pokémon comes near a Haunter, it will stalk the victim while floating and beckon it to come closer, whereupon it will then lick the victim with its gaseous tongue, inflicting convulsions on the victim that last until death. It has the ability to float through solid walls. Despite its predatory nature, it has been known to entertain and prank people in the anime. Additionally, it has even been shown to feel intense loyalty to a deceased Trainer. Haunter lives in dark, abandoned caves.
Haunter debuted in The Tower of Terror. After Ash befriended it, he attempted to use it to battle Sabrina in the hopes of freeing his friends in the process, but Haunter decided to goof off instead. At the end of Haunter Versus Kadabra, Haunter helped Ash succeed in his endeavor and decided to stay with Sabrina afterwards.
A group of Haunter appeared in Illusion Confusion!, along with a group of Gengar. They were causing trouble for Ash and his friends while they were wandering through a deep forest, by creating a number of illusions that impeded their progress.
In Fear Factor Phony, a Haunter was living in an abandoned mine with several other Ghost Pokémon. The Ghost Pokémon were having difficulty with the partying Psychic Pokémon living nearby.
A Haunter appeared in PK15. It was one of the residents of a spooky house.
A Haunter appeared in Scary Hospitality!, under the ownership of Lon. It was used alongside Lon's Gastly and Gengar to scare visitors of the "Scary House". This included Ash, his friends, and later Team Rocket.
In The Electric Tale of Pikachu, Ash encounters a giant Haunter called the Black Fog, notorious for using its Dream Eater attack to kill people and Pokémon by stealing their souls. Sabrina has a vendetta against this Haunter, as her Pokémon were attacked and killed by it when she was eleven, but she falls victim as well in her attempt to protect a team of people trying to hunt it down. With the combined effort of Ash and the team of hunters, the Black Fog managed to be weakened enough for capture, only for it to promptly use Selfdestruct, making itself faint right before Ash's Ultra Ball reaches it.
Pokémon Pinball: Two Haunter appear in a bonus stage accessible from the Red Table. Once the player knocks out the three Gastly, the pair of Haunter appear, and upon knocking them out, the player must then proceed to defeat the Gengar that appears.
No other Pokémon have the same type combination as Haunter and its evolutionary relatives.
Due to its unique type combination, Haunter and its evolutionary relatives are the only Poison-type Pokémon that are weak against Dark-type moves.
Haunter is the Pokémon with the most cry changes throughout the series, having been changed in generations II, III, and VI.
Haunter is possibly based on the dila, a spirit that passes through walls then licks certain humans to death according to Filipino mythology. It also appears to be based on a generic sort of cartoonish ghost. Like Gengar, Haunter may also be based on the Cheshire Cat, as it possesses what may be pointed ears, a large, toothy grin, and the ability to vanish at will.
Haunter is derived from haunt, as ghosts are known to do. It could also be a corruption of "hunter".