At first, Jack was the fairly likeable protagonist and a loving husband and father. He was a writer who accepts the job of winter caretaker for the Overlook Hotel, despite being informed of the building's grisly past and reputation as a cursed place (which he shrugs off as a superstition) and he takes his wife Wendy and son Danny with him to the hotel, thinking that the solitude of the place will help him in his writing as well. However, Jack soon descends into madness that is never fully explained, depending on the view of the audience he could've either suffered an intense mental breakdown or he was possessed by the spirits of the Overlook Hotel—whatever truly happened to the unfortunate Jack is never fully explained. Yet, the demonic possession is further implied by all the ghosts that haunt the hotel, especially the ghosts of young kids who frequently appear to Danny as well. The ghosts are apparently attracted by the boy's power and seemingly try to drag him into the underworld. Jack attempting to murder his family At any rate, Jack soon loses his mind completely, becoming increasingly abusive towards Wendy and Danny while holding conversations with a ghostly bartender (who appears to be the ghost of the previous caretaker) that apparently only he can see—he also has a traumatic experience with a ghastly phantom in a hotel room and ultimately descends into a murderous psychosis in which he tries to kill his wife and son with an axe (much as the previous caretaker had done years previously). However, Jack was outsmarted by his family after a fearsome manhunt, and ultimately left to freeze to death in the giant maze outside the hotel.
Differences between the novel and the 1980 movie
In the original novel, it is made quite clear that Jack slowly fell under the influence of the unspeakable evil force that appears to be the Overlook Hotel itself, or the demonic entity that took complete control of it and commands its ghostly population. The ghost of the former bartender often appears to Jack, explaining that he murdered his family upon the hotel's request and serving as the spokeperson between Jack and the hotel, which/who tries to hire Jack as well and make him do the same. At the end of the story, when Jack is completely controlled by the demonic entity, the narration no longer calls him "Jack," but as "the creature" or "the monster." It is clearly stated that the unfortunate Jack underwent an awful metamorphosis and is no longer human. "Jack" attacks his family with a roque mallet instead of his iconic axe and is destroyed alongside the hotel itself, which Danny, Wendy, and Halloran (the cook who works in the hotel, who also wields the shining) manage to destroy by detonating the heating system. Jack's possession is fully proven during the final confrontation between Danny and "the creature", when the boy manages to awake the spirit of his father with his Shining. Jack then bids a moving farewell to Danny and lets him escape.
The Shining (1997 TV Series)
Jack Torrance in The Shining 1997 series The TV series of the Shining follows directly to the novel as well as the roles of the characters and Jack. In this version, Jack is portrayed by Steven Weber.
The scene where he breaks down the door and yells "Heeeeere's Johnny!" was unscripted, yet kept in the film. In the sequel to The Shining, Doctor Sleep, it is revealed that during Jack's days as an English professor he had an affair with a student and she had a daughter named Lucy. Lucy would then have a daughter of her own named Abra who possessed a more potent version of the Shining.