In the novel
John Smith (b. 1947) experienced his first vision after hitting his head on an iced-over pond in 1953.
As an adult, he taught English in New England. After a date with his girlfriend Sarah to a county fair, he was caught in a car crash which sent him into a coma for four and a half years until May 17, 1975. When he regained consciousness, Johnny and his doctors swiftly discovered that, apparently due to seemingly minor brain damage sustained while he was in his coma – affecting his ability to remember numbers and addresses – a long-dormant part of his brain relating to touch had been reactivated, granting him the ability to touch people and objects and learn something about their pasts or futures.
Despite his use of these abilities only ever being benevolent, such as to warn a woman that her kitchen was on fire, Johnny eventually denied their existence, the only exception being when he was contacted by a sheriff seeking assistance in tracking a serial killer. Having found the killer, Johnny went into semi-retirement once again, taking a job as a private tutor when he found himself unable to return to his old teaching job on the grounds that he was 'too controversial' to be an educator. During a political rally, however, he shook hands with candidate Greg Stillson and foresaw an apocalyptic future that would take place if Stillson won the election.
Although reluctant to resort to murder, Johnny's hand was forced when he discovered that he had developed a tumour as a result of his accident, leaving him with only a limited time to live. With no hope of gathering evidence to expose Stillson's threat in the time left to him, Johnny instead purchased a sniper rifle and attempted to shoot him at a town hall meeting. Although Stillson survived and Johnny was killed by his security force, Stillson's reaction to the attack – particularly when he grabbed a child and attempted to use the boy as a shield – ruined his election chances for good.
Johnny discovered this altered future by grabbing Stillson's leg briefly before he died.
In the film
The movie essentially tells the story the same way it is described in the novel.
In the TV series
John Robert Smith (played by Anthony Michael Hall) was born in 1970, and experienced his first vision after hitting his head on an iced-over pond in 1976. He is the grandson of John Smith, after whom he was named.
He´s the protagonist of the series, which tells the story only partly like it is described in the novel, but the confrontation between Stillson and him is essentially the same without time going out like in the novel.
As an adult, Smith taught biology at Cleaves Mills High School until a horrific car crash on 6 June 1995 – the night he intended to propose to his girlfriend – put him into a six-year coma. Smith awoke suddenly on 1 September 2001, the day that Greg Stillson was sworn into office as a member of the Maine House of Representatives.
With the aid of physical therapist Bruce Lewis, Smith slowly recovered the use of his atrophied legs. During his recovery, Johnny learned that he had developed an extra-sensory perception while in his coma, giving him the ability to see a person's future or past upon physical contact. He later learned that, during his coma, Sarah had married Penobscot County Sheriff Walter Bannerman, and given birth to Johnny's son, J.J. Bannerman, whom Walt was raising as his own.
Sheriff Bannerman reluctantly employed Smith's abilities to stop a serial killer who turned out to be a member of Bannerman's own Department. Smith returned briefly to work at CMHS before retreating to his home with the intention of becoming a recluse, though he continued to use his ability to do consulting work for Bannerman and the Cleaves Mills Police Department. He also utilized his psychic power in a variety of cases, such as serving jury duty, uncovering the truth about his mother's death, and negotiating a hostage situation during a bank robbery.
Later that year, Smith met Congressman Stillson at a Faith Heritage rally, and experienced his first vision of Armageddon. Thence forward, his attention became focused on Stillson and finding a way to prevent the nuclear destruction of Washington, D.C. that he had foreseen.
In the midst of investigating Stillson, Smith continued to work with Sheriff Bannerman on local cases, including the rescue of a group of teenagers who became trapped in a mine once owned by Smith's own grandfather. After Bannerman was injured in the operation, he fell into a coma, and Smith used his ability to help revive him.
Smith later attempted to help Stillson's political rival, Harrison Fisher, win an election in order to derail Stillson's career, but Fisher winds up dropping out of the race because of a war-time atrocity that Johnny inadvertantly helped bring to the surface. Smith was also kidnapped by a group of documentarians, averted a plane crash, and worked with a psychic government project.
Smith also began to experience visions of a fellow psychic from the post-apocalyptic future named Christopher Wey, with whom he could communicate by way of his cane, which Wey had found in his own time. Through a unique method of "conference-calling," Smith realized that he could experience the future – Wey's present – though he lost the same amount of time that he spent in his vision from his own present.
Shortly thereafter, Smith became the prime suspect in the disappearance and murder of Stillson staffer Rachel Caldwell, but was ultimately cleared, and becomes involved with her sister, Rebecca. He later experienced a profound vision of the night of 6 June 1995, in which he psychically rescued himself from his own car-crash on the night he slipped into his coma.
While helping fellow psychic Bonnie Gibson escape the government project he formerly worked for, Smith discovered the date (though not the year) that the nuclear disaster in Washington, D.C. would likely happen – December 31st. He also helps Sheriff Bannerman track down a childhood friend who has become dangerous, encounters a pair of law students who are twins that have set out to prove that Smith's visions are legally unreliable, attempts to prevent a school shooting that may not take place for another decade.
As Smith's headaches and blackouts worsen as a result of his "conference-call" visions into the future with Wey, he is scheduled for brain surgery, but skips the procedure in order to prevent Rebecca from taking revenge on Greg Stillson for Rachel's death. On his way to Washington, D.C., he discovers how Wey came into possession of his cane in the future – his own future-self, blinded by the nuclear detonation, used it as a means to communicate with his past-self. Smith is told by his future-self not to interfere with Rebecca's plan, because the death of Greg Stillson will prevent Armageddon.
Despite the instructions from his future-self, Smith manages to reach Washington, D.C. before Rebecca can carry out her plans, and the two discover the truth about Rachel's death. Refusing to be manipulated by future events, Johnny throws his cane into the Potomac River, eliminating his ability to share visions with Wey or his own future-self, yet setting the stage for Wey to find the cane in his own time.
Smith later worked with fellow psychic Alex Sinclair to stop a grieving father from taking revenge on the people who sees as responsible for his son's hospitalization, and subsequently saved Sinclair's life as well. Smith also reunited with a former student, Dr. Alex Connors, and discovered that a project that Connors was working on was related to the nuclear destruction he had seen in Stillson's future. Connors eventually destroyed his laboratory, dying in the process, in order to stop his work from being used by Stillson, but his research was salvaged by a technician and sold to Malcolm Janus.
Smith reunited a musician, believed to be dead, with his son, saved a former police officer from being wrongfully executed, and uncovered an illicit cadaver-selling scam at the nursing home where Sarah's father resides. Smith also learned that his father had been institutionalized when, as a child, Johnny had told him of a building collapse he had foreseen. He later works with Stillson to find Stillson's girlfriend, Miranda Ellis, after she goes missing at sea, and learns that she tried to leave him after he confessed that he had killed his father after learning that his father had killed Rachel Caldwell.
After a confrontation in the Faith Heritage chapel resulted in the deaths of both Walt Bannerman and Malcolm Janus, Smith discovered that Stillson's future was changed – the nuclear disaster that destroys Washington, D.C. has been averted. With Bannerman's death, Johnny begins playing a bigger role in Sarah and J.J.'s life, moving them into his house. When Sarah discovers that Smith foresaw Walt's death and lied to her about it, however, she moves out and reconnects with Stillson.