In their original plan for the series, Grant and Naylor had specified that there would be no aliens and no robots. However, following the success of the first appearance by the Kryten character, Naylor convinced Grant to bring him back.
In the character's first appearance, originally only intended as a one-off, Kryten was played by actor David Ross but the popularity of the character meant that Kryten was introduced as a regular in Series III. The intention was to bring Ross back to play the role, but he was not available at the time and the position was filled by Northampton-born actor Robert Llewellyn, whose performances as Kryten in series III-VIII resulted in even greater popularity of the character.
Kryten was built by the corporation DivaDroid International in 2340; one of a number of Series 4000 models based on a design by Professor Mamet, a roboticist (played by Jenny Agutter). This design was actually intended as a joke on Mamet's ex-fiancé, John Warbuton, the mechanoids being a caricature of his fussiness and pomposity. All negative emotions such as jealousy, guilt, envy, frustration, and insecurity build up in a "mind negadrive", which when full would cause the head of the Series 4000 mechanoid to literally explode. This was supposedly a likeness to when Warburton would "blow" .
Kryten is hard-wired to obey all of Mamet's orders without question, so when a Psiren impersonated Mamet and ordered Kryten to crush himself in a garbage compactor, he had no choice but to comply. His reply upon emerging, having been compacted into a cube: 'I'm almost annoyed!' . Before Kryten left the Solar System, he was made to attend "toilet university", as he would remind people. This was however revealed by Kristine Kochanski to be merely a piece of software which ensured Kryten was thorough in his cleaning of lavatories .. Nevertheless he still had to take an exam to ensure that it was properly installed.
Kryten originally left the Solar System aboard a ship destined for Deep Space, the SS Augustus, and served aboard the vessel for decades. Not much is known about these years of Kryten's life, except that the human crew of the SS Augustus all died of old age, leaving Kryten alone for an unspecified amount of time .
Sometime after this, Kryten was picked up by the crew of the Nova 5 and he became the personal servant of three female crew members of this vessel. The Nova 5 crashed into an asteroid and for millennia, perhaps even millions of years, Kryten refused to believe the crew were dead and continued to wash and iron their clothes, dress them, and put out meals in front of their remains, all the while preserving their skeletons. It was from these long years alone that Kryten developed a phobia of being left alone, or human crews deserting him. Kryten's rigid belief in "Silicon Heaven", the electronic afterlife, kept him going - the idea that he would be rewarded for his servitude in the afterlife, where humans would instead become the servants. Kryten was eventually rescued by the crew of Red Dwarf where he is now reduced to serving the slobbish Dave Lister (to some extent at least), the only surviving human crew member on that vessel, indeed probably the sole surviving human in the universe .
It is possible that Kryten was inadvertently responsible for the accident aboard the Nova 5. In the first Red Dwarf novel, Infinity Welcomes Careful Drivers, the Nova 5 crashed because Kryten washed the navigation computer with soapy water. However, it is unclear whether or not this is canon in the Red Dwarf universe; there seems to be debate as to this subject amongst fans. It is mentioned by Dave Lister, however, in the television series that the accident aboard the Nova 5 was Kryten's fault .
Kryten (as portrayed by David Ross) was introduced in the first episode of the second series, in which he was only supposed to be a guest star . Initially, Arnold Rimmer took advantage of his servility, getting him to paint a grand portrait of Rimmer. Dave Lister however persuaded Kryten to rebel against his programming (which included showing him the movies Rebel Without a Cause and Easy Rider) and to become independent. Kryten changed the portrait of Rimmer to make it appear as though he was sitting on the toilet, and then poured soup onto Rimmer's bed sheets. Kryten took Lister's space-bike and went out to find a planet with an S3 (or Earth-like) atmosphere he could grow a garden, which had always been a dream of the robot's.
Kryten did not appear in the rest of the second series. However the character proved popular amongst fans of the show, and so the decision was made to bring him back at the beginning of the third series and make Kryten a permanent member of the Dwarfers. David Ross was unavailable, and so Robert Llewellyn was brought in to play the character.
A very fast scrolling text at the beginning of the third series (a parody of the Star Wars opening crawl) explains that Kryten smashed the space-bike into an asteroid. Lister found Kryten's remains and had to rebuild him from scratch, and so was unable to recreate him exactly. This was intended to explain the differences between Ross' portrayal of the character and Llewellyn's, as well as Lister needing to help Kryten break his programming all over again. Most noticeably, whereas he previously had an "English butler" voice, similar to C-3PO, he now spoke with what Llewellyn admits to be a bad Canadian accent.
In the episode DNA, Kryten is transformed into a human being using the organic material used in his construction as a template. However he quickly decided to change himself back into mechanoid form, because he didn't like his time as a human. This was due to the fact his nipples couldn't pick up radio waves (specifically "Jazz FM"), his eyes didn't have a digital zoom capability, power leads didn't fit in his anus properly when he tried to recharge himself, and he got erections when looking at photos of kitchen appliances.
In the seventh series, Kryten discovered that he has a "brother" named Able (also played by Robert Llewellyn, who co-wrote the episode), named in reference to the Biblical Cain and Abel. Kryten originally rejected the wastrel, drug-addicted mechanoid before an act of supreme self-sacrifice convinced him of his brother's worth .
In the eighth series, Kryten becomes a prisoner in Red Dwarf's Tank along with his friends. He is classified as a woman due to his lack of penis and sent to the woman's wing. He becomes friendlier with Kristine Kochanski while there, but is still desperate to correct the situation. He builds himself a makeshift penis from an old electron board, a toilet roll, some sticky back plastic, and an Action Man's poloneck jumper. He names his penis "Archie", and tries to teach it by getting it to jump through hoops. "Archie" however goes bonkers around the prison wings and many prisoners mistake it for a haywire mouse .
In the final episode of the series, Red Dwarf is attacked by a corrosive chameleonic virus. Kryten and his fellow Dwarfers are abandoned aboard the rapidly decaying Red Dwarf. To develop a solution, Krytan builds a prism based laser, which if concentrated on a mirror, creates a portal to a reverse universe, in the hopes of discovering an alkaline to cancel out the virus' effects. The machine successfully transports Rimmer to a reverse universe but breaks soon afterward. As the damage to the ship becomes irrepairable, Kryton, Lister, Kochanski and the Cat fix the machine and cross into the mirror universe to escape, Rimmer would later become stuck onboard the dying Dwarf as the virus destroys the prism. Kryten's fate beyond this is left unanswered.
Kryten has also extended his emotional range, which has led to him deactivating his shutdown disk (DivaDroid believes in planned obsolescence), although the crew were then forced into a showdown with his would-be replacement. His greatest ambition is to be human, and to this end he has attempted to learn to lie and insult people (mostly Rimmer), although he has trouble with the words "smeg head" (the best he can manage is "smeeeeeeee heeeeeeeee"). He did however become human for a few days after a machine changed his genetic structure, but he didn't enjoy the experience as much as he thought he would. He was briefly returned to factory settings (including the English accent) in Series VIII, but his hard-won independence broke through after the crew jogged his memory. When Red Dwarf was re-built with the crew, Kryten was reclassed as a woman due to his lack of male genitalia (that is, his lack of any genitalia: the only mechanoids given genitals were the ones created to work on Italian starships, as it was felt it would be psychologically comforting if the androids could stand around cupping themselves all day like their crewmates). Due to this deficiency, Kryten decided to make a penis called Archie, who runs around like a mouse. Kochanski commented that Kryten was a real man because "like all men, you have absolutely no control over your penis," thereby making Kryten very proud.
Perhaps the most significant element of his personality is guilt. When his ability to feel guilty for his actions is compromised in some way, he can become careless, rude and even aggressive. This guilt is not necessarily balanced out by a sense of pride in the good work he does - in the episode 'The Inquisitor', he believed his selflessness was purely a matter of programming and therefore he had not led a worthwhile life.
Kryten had at least three spare heads, one of which has droid-rot (a condition similar to computer senility) that gives it a Lancastrian accent. The spare heads can engage in conversation with Kryten. Once, the other heads held a poll and voted Kryten as the ugly, big-eared one, upsetting Kryten. The others took turns being head head. All of these were destroyed due to the final step of Mamet's joke; eventually a 2X4B mechanoid will "blow its top" (due to Lister wanting to put ketchup on a lobster). The "negadrive" which caused this has been removed, and, luckily, Kryten's personality chips survived and were placed in a new head. It is not made clear whether or not the personality chips of his spare heads were destroyed.
Kryten thinks that his middle name "2X4B" is jerky ., but says he once knew a "poor sucker" of a mechanoid whose middle name was "2Q4B".
Kryten formed an irrational dislike of the new Kristine Kochanski when he first met her, mostly out of a fear that she and Lister would fall in love and abandon him. However he grew to respect her (although not necessarily like her) after she saved Lister's life from the Epideme virus.
One of the best instances of how Kryten's personality was developed was how he commented on many of The Cat's fanciful escape plans:
Robert Llewellyn writes in his book The Man in the Rubber Mask that before settling on a Canadian accent, he, Rob Grant and Doug Naylor considered Swedish and American. Llewellyn discovered the Canadian accent while spending time in Vancouver, British Columbia, Canada; which he describes as being a cross between Scottish and American. The Kryten make-up was a constant source of discomfort for Llewellyn, as the prosthetic rubber mask required him to be in make-up for up to six hours. By Series VII, this had been reduced to two hours.