The television series Farscape features an extensive cast of characters created by Rockne S. O'Bannon. The series is set aboard a living spacecraft named Moya of the Leviathan race. The physical, racial and species-specific cultural characteristics, as well as underlying mythological/sociological similarities and differences of the alien races portrayed in Farscape were conceptualised and created by Jim Henson's Creature Shop.

John Robert Crichton, Jr. /ˈkraɪtən/, played by Ben Browder, is an International Aeronautics and Space Administration (most commonly referred to on the show as IASA) astronaut who, in the opening few minutes of the pilot episode, is accidentally catapulted through a wormhole across the universe, thus; setting the scene for the show as a whole. As the only regularly appearing human on the show, he is the main focus and is the main character as he narrates the weekly credits and is the only character to appear in every episode. Along with Michael Shanks's character of Daniel Jackson in Stargate SG-1, Browder's Crichton has been called one of the sexiest male characters in science fiction.

Although Crichton is a heroic and unwaveringly loyal character, he is also a mischievously comical one, so much so that he is the primary source of humor for the series. The show derives much of its humor from Crichton's habitual (and extensive) use of Earth-related pop culture references, often used as witty mockery in the face of danger or opponents who, being unfamiliar with the references, are unaware that they are being insulted. Although an occasional reference will provoke curiosity or confusion to his friends, Crichton's fellow shipmates are largely unaffected by these comments because they simply assume them to be native Earth terms that cannot be interpreted by translator microbes and merely extrapolate the meaning from its context.

Information about John Crichton's life before the first episode is only revealed slowly over the course of the series. He was the middle child born to Jack (an astronaut) and Leslie Crichton. He has two sisters, Olivia (his younger sister) and an older sister, Susan. He has a childhood friend named Douglas "D.K." Knox. John's mother died of cancer four years before his Farscape One accident. John Crichton followed in his father's footsteps by becoming an astronaut, flew on two missions prior to the Farscape incident and was Mission Commander on one of those missions.

In the first episode of season one, during a test flight designed to prove a scientific theory concerning the use of planetary gravity as a means for spaceship acceleration, a wormhole appears, and John and his "Farscape One" module are pulled into and through it. On his exit from the wormhole, he finds himself in the middle of a spaceship dogfight, during which he accidentally causes the death of Tauvo Crais, the brother of Peacekeeper captain Bialar Crais. Crichton's craft is pulled aboard a large spaceship named Moya, a Leviathan (a biomechanoid, i.e., a "living ship") where John meets his first aliens (Zhaan, D'Argo, Aeryn Sun and Rygel). Shortly after, John meets Bialar Crais, who wants revenge for his brother's death. John has to adapt quickly to a life with aliens, guns, and space travel, without the comfort of Earth culture. Toward the end of season one, Crichton encounters a mysterious alien race known only as The Ancients, who hide a repository of wormhole knowledge into his brain to guide him home, beginning a series-long chase by a Sebacean-Scarran hybrid Peacekeeper called Scorpius who hunts John and the rest of the Farscape crew to obtain that information.

Early in season two, Crichton learns that Scorpius has implanted a neural chip into his head, which causes hallucinations of a "neural clone" of Scorpius, whom he dubs "Harvey". These hallucinations influence Crichton in an effort to get at the hidden wormhole knowledge. As a result, Crichton's behavior grows more erratic and unpredictable, even as he continues to have romantic feelings for Aeryn Sun. In the end of Season 2, the neural chip takes complete control over Crichton (resulting in a Scorpius/Crichton mixed personality with extremely dark humor) and transmits a message to Scorpius. Shortly after that Harvey defeats Aeryn in an aerial dogfight and seemingly kills her. After Aeryn's death, Crichton regains control. The chip is removed, but stolen by Scorpius. With the beginning of Season three, Harvey still remains in Crichton's head and Aeryn has been revived by Zhaan, who consequently dies a few episodes later. Sometime thereafter Crichton is "twinned" by another alien; neither of the Crichtons can be called a copy, but are "equal and original" (and each has his own "Harvey") eventually, the crew of Moya is split across the two Leviathans, Moya and Talyn and they are subsequently separated from each other; each ship has one Crichton. The Crichton aboard Talyn begins a romantic relationship with Aeryn while the Crichton on Moya continues studying wormholes, helped by the repository in his brain. Jack the Ancient finds the Talyn Crichton, forcibly extracts Harvey and unlocks the wormhole knowledge, but this Crichton later dies of radiation poisoning from a wormhole weapon. When the survivors of the two crews are reunited, Aeryn (in her grief) is very cold to the remaining Crichton, due to him having different memories about the last few months; the crew members of Moya start going their separate ways at the end of season three. Just after Aeryn Sun leaves Crichton, seemingly for good, he learns that she is pregnant with his child (whether the child belongs to the Moya Crichton or the Talyn Crichton is left unknown).

Early season four leaves Crichton with nothing but time to work on his wormhole theories. He eventually reunites with the crew members of Moya, and Aeryn and Scorpius, who has fallen out of favor with Peacekeeper high command. Shortly, after arrival, Scorpius offers to remove Harvey. Due to the neural clone's longer presence within and increased familiarity with Crichton, Harvey's reaction includes persuasion and appeal to sympathy rather than threats. Crichton still agrees to allow Scorpius to remove the lingering neural spillover. Halfway through the season, Crichton finds his way back to Earth, but he voluntarily gives up the dream of Earth and returns to Moya. After a series of dangerous events (including Harvey's resurrection) Crichton and Aeryn find time alone together. Aeryn tells him he is the father of her child and Crichton proposes to her. The moment she accepts, an alien craft melts the two and ends the season.

Crichton and Aeryn are revived at the beginning of Farscape: The Peacekeeper Wars mini-series, and Crichton uses his wormhole knowledge to successfully force a peace treaty between the warring Peacekeepers and Scarrans. The wormhole knowledge in his brain is finally removed by Einstein the Ancient. During the mini-series, Aeryn gives birth to their son, named D'Argo Sun-Crichton in honor of their late comrade.