Haunter is a purple Pokémon with a gaseous body. It has a round head flanked by three large, spiked protrusions on either side. It has triangular eyes with small pupils and a mouth with a long, pink tongue. The gases composing its head curve into its mouth to form several pointed teeth. Disembodies hands with three clawed fingers each float in front of its body. Its body tapers into a jagged tail. Its gaseous form makes it one of the lightest Pokémon tying with Gastly, Flabébé, Cosmog, and Kartana. It can also float through walls.
Haunter hides in very dark places, such as caves, and is afraid of light. If a human or a Pokémon comes near Haunter, it will stalk the victim while floating and beckon it to come closer. Once approached it will then lick the victim with its gaseous tongue, inflicting convulsions in the victim that last until death. 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. In the past, Night Shade was its signature move.
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.
A Haunter appeared in Fear Factor Phony as a resident of an abandoned mining colony. 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 Haunting My Dreams, Ash encountered a giant Haunter called the Black Fog, notorious for using its Dream Eater attack to kill people and Pokémon by stealing their souls. Sabrina had a vendetta against this Haunter, as some of her Pokémon were attacked and killed by it when she was eleven, but she fell victim as well in her attempt to protect a team of people trying to hunt it down. With the combined efforts of Ash and the team of hunters, the Black Fog was weakened enough for capture, only for it to promptly use Self-Destruct, killing itself right before Ash's Ultra Ball could reach 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".