Jack Skellington is the "Pumpkin King" and de facto leader of Halloween Town. He is responsible for coming up with new and exciting ideas for each year's Halloween festivities. He first appeared in Tim Burton's The Nightmare Before Christmas. He has appeared in all games of the series aside from Kingdom Hearts Birth by Sleep, Kingdom Hearts coded, and Kingdom Hearts 3D: Dream Drop Distance.
 Kingdom Hearts
When Sora, Donald, and Goofy arrive in Halloween Town, they discover that Jack has decided to use the town's newest arrivals, the Heartless, to take terror to a new level for the year's festival. In an attempt to make the Heartless dance with him, Jack enlists the services of Doctor Finkelstein to create a guidance system to coordinate their movements. Unsatisfied with the results, Jack decides they need a "heart".
Sora offers his help in constructing the heart, unlocking the heart-like container for Doctor Finkelstein, and Jack accompanies Sora and company in gathering extra ingredients. When the Heartless become hostile following the doctor's first attempt at using the heart, Jack fights alongside the others.
Sora, Jack, and the others obtain the remaining ingredients for the heart, including "memory" from Sally, who asks Jack in vain to reconsider using the Heartless. They return to the doctor's lab with the ingredients, but the finished heart is stolen by Lock, Shock and Barrel, and Sora, Jack, and company give chase. They follow them to Oogie's Manor, and although they fail to recover the heart before the pranksters send it to Oogie Boogie, they give the three of them a sound beating.
Upon confronting Oogie in his torture chamber, Jack demands the heart back, but Oogie swallows it and attempts to use its power to control the Heartless. The group defeat Oogie, but as they are heading back to town, Oogie fuses together with his manor, forcing them into battle again. After Oogie is defeated once more, Jack watches Sora lock the Keyhole of Halloween Town.
Back in town, Jack laments not listening to Sally, who tells him that they'll come up with a new plan for Halloween together. Jack gives Sora the Pumpkinhead keychain and invites him to visit anytime.
 Kingdom Hearts: Chain of Memories
A memory-based projection of Jack appears in the memory Halloween Town within one of the rooms of Castle Oblivion. When Sora and company enter, he makes a frightening entrance, scaring Donald. He takes the group to see Dr. Finkelstein in hopes of finding a way to get rid of the town's Heartless. The doctor sends Jack to retrieve his memory potion from Sally, and Sora comes along.
When they find Sally, she expresses concern of what would happen if someone drank the potion, while Jack is excited. When Oogie Boogie steals the potion and takes off, the group goes after him. They catch up, but Oogie drinks the potion, and they fight and defeat him. Back at the lab, after Sora turns down the chance to drink the leftover drops of potion, Jack tells him that fear and doubt are the signs of a strong heart, and he sends them on their way.
Sora can summon Jack during battle as a friend card.
 Kingdom Hearts 358/2 Days
While Roxas is engaged in a mission in Halloween Town on Day 149, Jack is planning the next Halloween festivities. He is at a loss for new ideas, but he gets some inspiration when he catches a glimpse of Roxas leaving the world through a Dark Corridor.
During his next mission to Halloween Town, Roxas sees Jack presenting an idea to Doctor Finkelstein, decorated balloons that contain terrifying surprises. The doctor approves of the idea, although Jack is still not satisfied. Roxas later sees Jack and Zero in the Graveyard, where the ghost-dog shows Jack that some balloons contain Heartless. Jack figures that someone else has decided to place the Heartless in balloons to add an extra level of terror. Jack continues brainstorming, hoping to prevent this other individual from coming up with better ideas before him, and when he gets a new idea, he gives Zero a bone and heads for Dr. Finkelstein's lab.
When Roxas returns on a later mission, Jack has had the Doctor build giant lanterns for him to use for grand entrance. Although he still isn't satisfied, he is further inspired by the explosion when Lock, Shock, and Barrel blow a hole in the wall of the Graveyard.
Roxas returns for Mission 62 to see that Jack has had Dr. Finkelstein create a freezing pumpkin-bomb. The Doctor approves of Jack taking inspiration from the world around him. The two briefly discuss the activities of Lock, Shock, and Barrel, but neither of them know what they are up to.
Jack witnesses from a distance the battle between Roxas and the Leechgrave during Mission 66, and seeing Roxas's black coat and the Tentaclaws give him an idea. By the time Roxas returns to the town square, Jack has erected a scarecrow combining the two images, with plans to make more. Although Dr. Finkelstein is impressed, Roxas is less so.
 Kingdom Hearts II
One day while walking through the Hinterlands with Zero, Jack discovers a clearing with trees decorated with festive doors. He opens a door shaped like a Christmas tree and falls through into Christmas Town.
When Sora, Donald and Goofy arrive in the Town Square, which is decorated with Christmas lights, Jack arrives in a makeshift sleigh pulled by skeletal reindeer. He wishes them a Merry Chistmas and tells them that he running Christmas "again". They visit Sally in Dr. Finkelstein's lab before Jack heads off to bring Santa Claus, but he comes back to tell Sora that Heartless have appeared in town. Jack helps the group defeat the Heartless and asks them to be Santa's bodyguards. They all travel to Santa's House in Christmas Town, but Santa is less than pleased to see Jack after the last time he tried to run Christmas.
When Lock, Shock, and Barrel invade Santa's factory with Maleficent's help, Santa sends the group after them, and they follow the pranksters to Curly Hill where they defeat the Prison Keeper. When Lock, Shock, and Barrel run off to see Oogie Boogie, Jack and the others are surprised to learn that he has been revived. On their way back, Sally tells them that Oogie has kidnapped Santa Claus and is headed for Christmas Town. They return to the Toy Factory, where they defeat Oogie Boogie.
Afterwards, Sally gives an excited Jack the Santa costume she had been working on, but Santa convinces him that they should each stick to doing the jobs they love and do best, and Jack, newly inspired, heads towards Halloween Town with the Mayor, who has come looking for him. As he leaves, his costume reveals the next Gate.
When Sora, Donald, and Goofy return to Halloween Town, they find Jack, still in costume, picking presents off the ground in the Hinterlands. Although Sora is skeptical, Jack explains he just found the presents and is only returning them to Santa. When they arrive at Santa's House, Santa informs them that a large number of presents have been stolen from his factory, and Jack volunteers the group for finding the thief. Although they find Lock, Shock, and Barrel in the Wrapping Room, they claim they are only looking for parts for Dr. Finkelstein's experiment and have no interest in Christmas presents.
Sally arrives with news of Heartless with presents in Halloween Town, so the group return and recover the gifts, only to discover the Doctor's experiment has also been stolen. Jack decides to set a trap for the thief using decoy Christmas presents, and they discover the thief to be the experiment itself. In gratitude, Santa lets Jack ride with him in his sleigh. After Jack returns, Sally helps him realize that meaning of giving a present is not the gift box, nor the present inside it, but the wish to make someone happy, and the two dance in the snow.
Some time after Xemnas's defeat, Jack is seen, sans costume, discussing plans for the next Halloween with everyone in the Doctor's lab.
Jack is shown to be incredibly eccentric, always alive and active. He is somewhat of an optimist; when he puts his mind to something, he will not stop until he achieves it. He tends to be slightly oblivious, and never thinks things through, which usually leads to disaster. However, he is a generally cheerful character who is greatly respected by all, with the exception of Oogie.
Jack is an extremely thin and equally tall being, his legs being over twice as long as his torso. He is a skeleton, and so his head lacks hair and sports empty eye sockets and nostrils. Strangely, his neck is solid, not showing vertebrae segmentation. His skull is similar, showing no distinction between his upper and lower jaws. His mouth is thin and wide, marked by a number of small "seams", similar to a Glascow smile. Jack is missing several teeth in a number of different places. Unlike his head and neck, Jack's hands do show joints.
Jack's usual attire is a macabre black suit with white pinstripes. The top has a single white button, and a white shirt is visible underneath. His black dress shoes are bizarrely small in comparison to the rest of his body. The coat tails of Jack's coat reach to about knee-length, and he wears a large, black bow-tie shaped like a bat with several white veins in its wings and white eyes.
When masquerading as Santa Claus, Jack dons an obviously fake white beard (the part of the beard that should attach to his chin dangles a few inches from it) that reaches to the top of his thighs. His faded red pants have a vertical seam on the front, and his black, knee-high boots have fur lining at the top. Jack's tails in this outfit are about the same length as his normal ones, and he wears a maroon belt around his waist. His long sleeves are also fur lined at the cuffs. Finally, his faded red Santa hat also has white fur lining around the rim and a white fur ball at the tip.
Because of Jack's extreme height, he doesn't need to run to keep up with Sora. Instead, he is seen speed-walking throughout the series.
 Kingdom Hearts
Jack cannot equip a weapon, but his attack power and MP is still fairly high. Jack instead attacks using his magic, which is similar to Sora and Donald's, but has a Halloween theme to its animation. Jack has two equipment slots, and three item slots. Jack's abilities are as follows:
 Kingdom Hearts Re:Chain of Memories
Jack is called to fight with his friend card that can only be summoned in Halloween Town. He uses magic like Donald. If you stock more of his cards, the higher level of magic he will cast. Below are the sleights that the Jack (card) can be used in:
 Kingdom Hearts II
Jack is a mage character and fights using his magic, which is similar to Donald and Sora's, but with a decisively Halloween theme—his Fire magic for example, manifests as three blazing pumpkin heads. As such, his ability list is very similar to Donald's and he tends to burn through his MP quickly. Jack has no armor slots, two accessory slots and three item slots. His "weapons" are his own fists. Jack's abilities are as follows:
Jack originally appeared as the main protagonist of Tim Burton's stop-motion animated classic, The Nightmare Before Christmas, and his is role almost identical to that of his role in Kingdom Hearts II. Being bored with Halloween, Jack goes for a walk in the woods and uncovers Christmas Town. Amazed by its magic, he decides to take over Christmas with disastorous results, but he eventually saves the day. Chris Sarandon reprises his role as Jack in Kingdom Hearts and Kingdom Hearts II.
 See also