Jack O'Lantern, or simply Jack, is the very first chachaoong and the first King of the Chachaoongs. Not very much is known about him except that to all the other chachaoongs, he is like a god that walks among them. His right-hand man is Chuh-Yong, who helps him with various tasks such as dealing with other chachaoongs who cause trouble. Jack does not seem to intervene much personally—but will do so if the situation calls for it.
Jack appears as a serious young man with long white hair and large grey eyes. He also wears a large black robe covering the lower part of his body. Despite the fact that the rest of the chachaoongs are vastly intimidated by him, his figure is not very imposing. He has a very slight build and, according to the author, stands at only about 5'3" tall. Regardless of his less-than-imposing physical appearance, simply being in his presence is enough to bring most other chachaoongs to their knees, or even render them unconscious.
Jack is an extremely mysterious figure. He has only been shown a few times, never smiles, and rarely speaks. He has quite the intense glare and does not seem to have a problem using his presence to intimidate people into submission. He was compassionate enough to allow Chuh-Yong the benefit of not dealing with Mu-Young and Ignatio, as Chuh-Yong had personally raised them and was emotionally attached to them. It is unclear if this was simply Jack's kindness to his subordinate or if he is unconcerned with the mutation that caused the twins to be born (it is possibly due to Yu-Jin asserting that mutation would not impact the second generation, or it could simply be because Jack feels it is not his place to be concerned about the second generation.)
Jack has a large, multi-legged, skeletal beast that seems to stay near him at all times. It is unclear if this beast is his yongma, or something else. It is unclear what powers it may have; so far, it has only been seen sitting, walking, holding a lantern, and materializing two large scrolls containing lists of chachaoong names out of Jack's cloak.
Jack's powers are still a mystery, however, Bigak states that beyond being the First Chachaoong, Jack's ability is the reason he is deified. His presence is so overwhelming that most chachaoongs can barely stand in his presence, much less remain conscious. Further, if Jack calls a chachaoong's name three times, that chachaoong's name is crossed off of a list that Jack's skeletal beast holds, and the chachaoong whose name was called immediately dies. Because of this ability, Jack effectively holds all the chachaoongs' lives in his hand. Nevertheless, Bigak reveals that Jack is not as strong as he once was, implying this is because the first generation is drawing to a close.
- Chuh-Yong - He is essentially Jack's second-in-command. He seems to handle most of the work as far as actually watching over and dealing with issues in chachaoong society, and has said that he still can never tell what Jack is thinking, and does not know much about him, despite their years together. Nevertheless, Jack seems to understand Chuh-Yong's thoughts and feelings very well.
- Yu-Jin - Though they have only interacted once within the story, it's implied that Jack and Yu-Jin may have known each other previous to Yu-Jin's current existence. Jack specifically chose Yu-Jin to be the next king. Their interactions during their one meeting were ambiguous but it's clear even Yu-Jin in his awakened form had difficulty withstanding Jack's presence.