He first appears as the main antagonist in Casper: A Spirited Beginning where he runs Ghost Central with his sidekick Snivel who realize that Casper is missing. Kibosh is furious, worried about how he'll look if some rookie ghost is wandering about without any proper schooling. Kibosh orders Snivel to find Casper and bring him back to Ghost Central.
While Casper was being trained by the Ghostly Trio, Snivel called up Kibosh and told him that he's found Casper with the Ghostly Trio and that the trio are teaching Casper unorthodox and illegal ghostly techniques. The trio are planning to use Casper to put Kibosh in his place. Kibosh is outraged.
The Ghostly Trio lose Casper and Kibosh arrives at Deedstown and locks them up in a cage. He then goes to the Applegate Mansion to find Casper. Casper eats a bomb and saves his friend, Chris. Kibosh is impressed with Casper's actions and allows Casper to stay with his so-called uncles and leaves them in peace.
He and Snivel later appear at the start of Casper's Haunted Christmas when he is accidentally summoned by the Ghostly Trio via a magical whistle they stole from Snivel, which makes him angry. Kibosh then points out that Casper must scare at least one person a year, or he and the Trio will be banished to "The Dark" for all eternity. He then revokes the Trio's haunting licenses to keep them from scaring until Casper scares someone by Christmas Day morning, and sends the four to Kriss, Massachusetts with a cannon, and laughs after they blast off.
He next appears when Stinkie receives a "message" on his laptop and opens it, with Kibosh emerging from the screen, scaring the Trio. Kibosh reveals that he's having Snivel keep an eye on them to keep them out of trouble until Casper scares someone. Fatso believes that he can, so that they get their haunting licenses back. Kibosh laughs at the idea of Casper saving his uncles' "sheets", and then reveals that he will give either peace or doom the next time they met.
At a late point in the film, Casper finally decides to scare the Trio to keep them from ruining Christmas. To do this, he had to think of what scares them the most, which of course is Kibosh, so he, Spooky, and Pearl work together to build a Kibosh decoy from the Jollimores' Santa decoration. Casper then provides the voice of Kibosh to lure the Trio and scare them, which works. He accidentally says that Holly is cute, but fortunately, the Trio doesn't notice what's going on. Despite this, Casper panics and pulls the cord of Christmas lights by mistake, and the mechanism shuts, confusing the Trio. Casper throws the cord to Pearl, who in turn throws it to Spooky. Spooky then flies to the outlet and plugs the cord back in, and this creates a power surge, electrocuting him and the decoy, making the Trio think Kibosh is attacking and they run off, but soon they realize that they were tricked and run back to get their revenge.
Spooky accidentally tips the decoy over, and Snivel, who was trapped in the exact same object by the Trio, emerges. Casper then grabs Snivel's magic whistle and blows on it, summoning Kibosh who unnoticingly destroys the Santa/Kibosh decoy, right before the Trio come back. But they still think that Kibosh is a fake, and assault him to the point that they push him hard on a red carpet and have him rolling nonstop on the road. It is only then that when Kibosh returns that they did panic, with Kibosh furious about what they did to him. Kibosh then proceeds to banish Casper, Spooky, Pearl, and the Trio, to "The Dark", but when Casper reveals that he scared his uncles using a decoy of him, he decides to set them all free. Snivel then discovers the "Time Boomb" that the Trio was using for a Christmas fright, which makes Kibosh angry at them for breaking his orders again. He then tries to banish the three to "The Dark", this time without Casper or anyone else, but the Trio confess, revealing that they just reconsidered using the scares and traps as a comedic torture on themselves instead of the townsfolk, as a Christmas present to Kibosh. They then use the traps for such and, as a climax, Stinkie eats the bomb, Stretch eats Stinkie, Fatso eats Stretch, and the bomb explodes, sending them flying. Stinkie then uses his foul breath to change the banner from "The Spirit of Scaring" to "The Spirit of Sharing". Kibosh sees the newly changed banner and praises their actions, and then has Snivel return their haunting licenses to them. Kibosh and Snivel then leave Casper and his uncles in peace once again.
- Kibosh was once a friendly ghost at Casper's age, revealed in Casper's Scare School.
- It turns out that Kibosh is completely unaware that ghosts like him are actually spirits with unfinished business, and that those without unfinished business cross over to the next world. If he learns about it, it is possible that he might reform.
- He was voiced by James Earl Jones in Casper: A Spirit Beginning, and later Colin Murdock in Casper's Haunted Christmas and Kevin Michael Richardson in Casper's Scare School.
- Kibosh is arguably the most iconic villain in the Casper the Friendly Ghost franchise being that he appears in many incarnations where is in film, television series, games, and comic books.