John Kramer was originally employed as a toy maker, living a relatively dull, average existence content that there was always time to achieve goals tomorrow. He was often afraid to make commitments, to the point where his girlfriend broke up with him when he wasn't willing to further their relationship. Though he realized that there were more opportunities in life, he was simply too lazy and complacent to pursue them until a tragic discovery changed his life.

John rapidly grew ill, returning home every evening to vomit; he became weaker as his symptoms became more severe. John was diagnosed with an inoperable frontal lobe tumour and cancer, forcing him to face his own mortality. He began to realize how fleeting and valuable life truly was. Becoming more attentive to other peoples lives as his own diminished, John saw how they took their lives for granted and was disgusted.

At the hospital, he witnessed various people who, in his opinion, were abusing their lives. Among them were Amanda Young, a young woman who had overdosed on heroin, and Paul, John's boss at the toy factory; Paul, who had a wife and kids, had attempted to commit suicide by cutting his wrists.

Utterly depressed at the futility of life, John attempted to commit suicide by driving his car over a cliff. John survived the crash however, clinging to the remnants of his life, however small. He discovered that only when he knew his death was impending did he really begin to value his life. As John observed other people wasting their lives, people undeserving and unappreciative of the life being denied to him, John began his mission to make people appreciate their lives and realize how precious life truly is, one person at a time.

John spent the next months of his life observing and planning meticulously for his "subjects", painstakingly creating devices to test their desire to live, often through ironic means. For example, Paul, the man who had slashed his wrists, was sentenced to crawl through a maze of razor wire in order to survive.

Placing his subjects in lethal traps, each victim was left a single chilling message explaining the 'crime' they had committed to deserve their fate and how they could escape. Each was conveyed either by a distorted voice or by Jigsaw's puppet, Billy. They often involved quick thinking, ethically difficult decisions and often self-mutilation that Jigsaw would often be present to view, unknown to the victim.

As his victims increased, authorities coined the nickname "The Jigsaw Killer" - or simply, "Jigsaw" - because of the jigsaw-shaped piece of flesh that he would cut from an unsuccessful victim. As John would later explain to Detective Eric mathews however, the piece was not intended to be used as a signature but simply to represent the 'piece' that the victims were missing; the survival instinct.

Jigsaw targeted a new victim, Amanda Young, the heroin addict he had met before at the hospital who he felt had thrown her life away when she had a whole life ahead of her. He first placed her in a lethal trap, which Amanda managed to pass and escape with her life. Though Amanda had been placed in the deadly trap, she felt as though Jigsaw had 'helped' her reconsider her life and how she had wasted it on drug abuse. After she returned home following police interrogation, Jigsaw confronted Amanda, seeing potential within her. Amanda agreed to become his apprentice, planning to take on his mantle when he eventually succumbed to his illness.

Jigsaw set about training Amanda to possess the beliefs and skills to carry on his legacy, struggling to help her cope with her emotional responses to the brutal nature of their work. The pair grew closer with Amanda being of great importance to Jigsaw and Amanda reciprocated these feelings.

Jigsaw's health continued to rapidly decline, gradually reducing his mobility as his body degenerated and withered, confining him to a makeshift hospital bed. He was forced to ensure that Amanda was ready for the task before her before he died, but he knew that she was already experiencing problems and not following the rules of Jigsaw's 'games'. Amanda had become a full-out murderer, creating traps that offered no salvation to its victims. Jigsaw could not let Amanda continue on this path when he died, so he prepared an elaborate test with which he could once again test his apprentice to decide if she could truly carry on his work.

As Jigsaw lay on his deathbed, Amanda, at his order, kidnapped Dr Lynn Denlon, testing her with the ability to keep John alive until another victim, Jeff Reinhart, could escape his test. To ensure Lynn's help, Jigsaw had Amanda place an explosive collar on her neck that was linked to his heart rate; it would explode if John died. Jigsaw struggled to cling to life and see his final test complete but his condition deteriorated rapidly, causing Amanda great distress.

Amanda's anxiety grew into hostility towards Dr. Denlon, jealous of the attention that Jigsaw was giving to her, intended or otherwise. As the tests continued, Amanda started to become increasingly unstable, eventually refusing to release Lynn from her trap when ordered to do so by Jigsaw. Jigsaw revealed his knowledge of Amanda's murders but begged her not to kill Lynn, saying that she was important to Amanda's own survival. Amanda admitted that she thought no-one really changed from the near-death experiences in Jigsaw's traps, which she used as her motive for the inescapable traps. Jigsaw continued to plead with his remaining strength for Amanda to release Lynn because he did not want anything to happen to Amanda, but she refused, shooting Lynn in the back just as Jeff appeared, having escaped his trap. Jeff retaliated by shooting Amanda in the neck.

As Amanda lay dying, a saddened Jigsaw revealed that Jeff was Lynn's husband, and that everything that had occurred was an elaborate ploy to test Amanda's ability to release victims who passed their tests; Amanda had failed. Though she meant everything to Jigsaw, there was nothing more Jigsaw could do for Amanda.

As Lynn lay injured, Jigsaw spoke to Jeff and offered him one last test. If Jeff could forgive Jigsaw for putting him through his traps, and learn to let the death of his son go, then Jigsaw would summon medical help for Lynn and Jeff could have his family back together again. Jeff forgave Jigsaw, but picked up a circular saw blade, slitting Jigsaw's throat with it. With his last breaths, Jigsaw pressed the play button on a tape recorder he was holding in his hand. It relayed a personal message, telling Jeff that he had learned nothing and was still motivated by vengeance. Jigsaw went on to explain that he had hidden Jeff's daughter in a secret location that only he knew, and the secret would die with him. Jigsaw then flatlined, activating Lynn's trap to fatal effect and locking off the exits to Jigsaw's lair, dooming Jeff to lose everything by failing the test. Jigsaw died, having completed his final test.

Jigsaw reappears in Saw V, in flashback meetings with Hoffman, attacking and kidnapping Paul Leahy, then setting up and later watching his razor wire trap from Saw, as well as setting up the house of Saw II. He is shown on his deathbed talking to Hoffman about setting up a test, which leads Hoffman to exit the room as Young enters with Dr. Denlon, which occurs near the beginning of Saw III. Jigsaw also appears in a video will to his ex-wife Jill Tuck, leaving her a mysterious box. His deceased body is shown several times during the start of the movie, which was also the end of Saw IV, an opening scene in which Peter Strahm receives his first cassette tape, and a flashback which occurs to Strahm later in the film.

Jigsaw appears in flashbacks in the film. One flashback set prior to the events of the first film showed that it was Amanda Young who sent Cecil to Jill Kramer's clinic to steal drugs for her. This resulted in Jill's miscarriage, and thus Young was revealed to be an indirect cause of John Kramer's transformation into Jigsaw. Further flashbacks set prior to the events of the first film reveal that Jigsaw targeted William Easton for one of his games because he had insensitively denied Kramer health coverage after he had developed cancer. In the present time of Saw VI, Kramer shows himself on video twice to Easton instead of the Billy Puppet (the method Kramer usually used to speak to his subjects), so Easton could look in the eyes of someone he let die. In another flashback, this time set between the events of the first and second film, Jigsaw explains to his ex-wife that his "rehabilitation" works, showing Amanda Young as supposed evidence of this. A flashback set just before the events of the third and fourth films explores the group dynamic between Jigsaw, Amanda Young and Hoffman. Jigsaw criticises Hoffman for not seeing the test subjects as human beings and also critiques his approach to setting up Timothy Young's trap. It was also shown that Jigsaw seemed to have had a closer emotional attachment to Amanda Young than Hoffman. Shortly afterward, Jigsaw gave his ex-wife the key which she later used to open the box he gave her in his will in Saw V. In the present time of Saw VI, it is revealed that the box contained six envelopes (marked 1 through 6), a thicker envelope, and an updated version of the "Reverse Bear Trap". She gave Mark Hoffman envelopes 1 through 5, but hid everything else from him and later delivered the thick envelope to an unknown person. Envelope 6 was meant only for Tuck-Kramer, instructing her to trap Hoffman and put the "Reverse Bear Trap" on him so he could be "tested". This fulfilled the promise made, via the audio tape discovered in the stomach of Jigsaw's corpse, that Hoffman would not go untested.

Bell reprised his role as John Kramer/Jigsaw in Saw 3D, though his role was extremely minimal compared to previous films. He is seen in a flashback meeting Bobby Dagen at his book signing, subtly calling him a liar. He then mocks him while getting his own copy signed, which is then used in the path of Bobby's game to remind him of their encounter. He appears at the end of the film, where it was revealed that after Dr. Gordon escaped the bathroom, Jigsaw dragged him away and gave him a prosthetic foot, and congratulated him for surviving. He then made Gordon his final accomplice, considering him to be his greatest asset. Gordon assisted Jigsaw in traps which required surgical knowledge. The contents of the package Jill left at a hospital in Saw VI was shown to be a video tape for Gordon, in which Jigsaw told him that should anything happen to Jill, he would have to "act on [Jigsaw's] behalf". It is implied that John knew Hoffman would rogue and start straying from his ideals and wanted him to be punished. After Jill is killed by Hoffman, Gordon fulfills this request by assaulting Hoffman and sealing him in the bathroom from the first film.