Jack Torrance is the main protagonist and was played by Jack Nicholson in The Shining.
He is portrayed more grimly in the 1980 film. In the novel, Jack is a tragic hero whose shortcomings lead to his defeat, while the film implies that he is insane from the start. It also omits his traumatic childhood.
The film's first major deviation from the source material occurs when Jack attacks Hallorann. Instead of merely injuring him with the mallet, Jack brutally kills Hallorann with an axe wound to the heart.
In the film, Jack hears Danny scream, and chases his son to a hedge maze outside the hotel (in the novel topiary animals come to life and threaten Danny). Danny erases his footprints, so his father won't be able to follow him. While Wendy and Danny escape the hotel in Halloran's Snowcat, Jack gets lost in the maze, rests from chasing Danny, and freezes to death.
While Jack redeems himself in the book, in the 1980 film, he succumbs to his demons and is ultimately damned. The film ends featuring an old black and white photgraph saying and showing' Overlook Hotel, July 4th Ball, 1921. A young Jack stands smiling in the bottom center.