Role in the film
Jack is a being made out of wood and pumpkin. He was created by Ozma to scare the witch Mombi. When Mombi took over the Emerald City with the aid of the Nome King, she imprisoned Ozma within a mirror, and disabled Jack by taking off his wooden limbs and left him in her attic, threatening to bake him into a pie. However, because she was wearing Head #22 at the time, she never bothered to come back for him as she would constantly change heads. Eventually, he would encounter Dorothy Gale, whom he mistakes for Ozma, and her chicken Billina. Dorothy helps put Jack back together, and thanks to his long arms, is able to open the door to the attic to help Dorothy retrieve both Tik-Tok and the Powder of Life. As part of Dorothy's plan, Jack helps Tik-Tok attach palm leaves and the head of a gump to a sofa so that it can fly the group to the Nome King's mountain. However, Tik-Tok begins to run low on his intelligence just when Dorothy obtains the powder but awakens Mombi, forcing them to hastily construct their creature and bring it to life. Though the sofa was not put well together, the group manages to fly away on the Gump and narrowly escape Mombi.
By morning, the Gump begins to fall apart, sending the group plummeting towards the mountain. Billina lands along with Jack in his head, and stays in there for safety. The Nome King then appears to the group on the front of his mountain, where Dorothy asks for him to let her friend the Scarecrow free as well as the citizens of Oz. The king laughs at her threat, as the ground suddenly starts shaking and crumbles, taking Dorothy along with it. Just when she appears gone, the rest of the group is suddenly brought to the throne of the Nome King with Dorothy safe and sound. The Nome King proposes to the group they play a game: if they touch the correct ornament and say the word "Oz" within three guesses, then the Scarecrow will appear and they can go free. But he does not tell them that if they fail to guess correctly, then the guessers would turn into ornaments as well. When it is Jack's turn, Jack sadly says goodbye to Dorothy who wishes him luck. Unfortunately, Jack fails to guess correctly, as he and Billina are turned together into an ornament. However, Dorothy manages to guess the correct ornaments correctly, and she anages to turn the Scarecrow, the Gump, and Jack (who was a green vase) back to normal. But then the Nome King appears, angered that Dorothy guessed correctly, stops the group from guessing and tries to eat them off. He picks up Jack, but as he tries to eat him, Billina, who was hiding in Jack's head, lays an egg that falls into the Nome King's mouth. The Nome King is horrified, and puts down Jack as he disintegrates from the poisonous effect of the eggs. As the mountain begins to collapse, Dorothy manages to retrieve her ruby slippers from his remains and wishes the group out of the mountain and for everyone in Oz to be revived.
They are instantly teleported outside the Emerald City, where the Ozians celebrate the defeat of the Nome King. When everyone wishes Dorothy to stay and rule as their queen, Dorothy reveals that while they are all the best friends she could ever have, she still has to go back to Kanses, as it is her home. When she wishes she could be in two places at once, the magic of the ruby slippers reveals Ozma trapped in the mirror, where Dorothy pulls her out of it and frees her. Jack exclaims with happiness to see his real "mom" again, as Ozma reveals herself to be the true ruler of Oz. After Ozma promises Dorothy she will be able to return to Oz another time, Jack says goodbye to Dorothy along with the other Ozians as Dorothy disappears.