Arnold Judas Rimmer is a fictional character and one of the main characters of the science fiction sitcom Red Dwarf, played by Chris Barrie. Rimmer is a second-class technician and the de facto leader of the mining ship Red Dwarf. Portrayed as snobbish, pedantic, and self-centred, Rimmer is unpopular with his crewmates and is often the target of insults and general ridicule.

After he is killed by a radiation leak during an ellipsis in the series' first episode "The End" (1988) Rimmer is present for most of the series as a computer-generated hologram, indicated by the 'H' symbol on his forehead. From series I-V, Rimmer is intangible as a hologram and unable to interact with his environment, referred to in-universe as "soft light". Come the series VI episode "Legion" (1993), Rimmer's Light Bee is upgraded by the titular character to a "hard light" hologram where he is now able to interact with his surroundings as well as being essentially indestructible, yet still able to feel pain. Following the character's departure in the series VII episode "Stoke Me a Clipper" (1997), Rimmer is absent from the show until series VIII, where a human version of Rimmer is shown having been resurrected by nanobots with no memory of the hologrammatic Rimmer's experiences and only those of Rimmer prior to the radiation leak in the first episode (likely from when he had his personality disc last updated before his death). Following a ten-year hiatus after series VIII, the character reappeared as the original hologram Rimmer in the miniseries Back to Earth (2009) onward. Doug Naylor confirmed in 2020 that the Rimmer from Back to Earth onwards is the original Rimmer having returned from his time being Ace Rimmer. Why he returned or what happened to the resurrected version of Rimmer from series eight has not been revealed yet. For a brief time in the feature-length special The Promised Land, Rimmer is temporarily upgraded to Diamond Light, a combination of both soft and hard light.

The creators of the series acknowledge that Rimmer's surname comes from a snobby prefect with whom they attended school. They joke that only the boy's name was used, and not his personality because "that would imply he had one".

Rimmer first appeared in Red Dwarf's first episode "The End" (1988), where he is characterised as second technician on board the mining ship Red Dwarf, ranking above Dave Lister (Craig Charles), the lowest ranked crew member on board the ship with whom he shares quarters, and below all four of the service robots. As a technician, Rimmer does maintenance work on vending machines that not even the robots are assigned to. Rimmer is shown having difficulty revising for his "engineer's exam" which he hopes to pass and become an officer after having failed before prior to the episode, and he reveals that he was not academically educated like others who had become officers. After Lister is awakened from stasis, where he was put as punishment for bringing an unquarantined cat on board, the ship's computer Holly (Norman Lovett) tells Lister that the ship's crew died in a radiation leak from a drive plate Rimmer had improperly repaired and Lister was kept in stasis until the radiation levels returned to normal three million years later. Rimmer is depicted as having been brought back to life as a hologram, having the same drives, feelings and emotions as the human Rimmer, but being unable to touch anything. The only other survivor on board Red Dwarf is a creature called "Cat" (Danny John-Jules), a descendant of Lister's pregnant cat who was safely sealed in the hold along with her unborn kittens during the radioactive crisis.

By the time of "Future Echoes" (1988), Rimmer claims to have taken the "astronavigation exam" without passing nine times, or ten, "if you count the time he had his spasm". He also claims in this episode that his father had said, "Shiny clean boots and a spanking short haircut, and you can cope with anything," right before "that unfortunate suicide business".

In "Balance of Power" (1988), Holly reveals that reason Rimmer was brought back as a hologram was because, in Holly's judgment, Rimmer was the best person to keep Lister sane because the two had "shared fourteen million words between each other", making Rimmer the crew member with which Lister had the most interaction; in Holly's judgment, the fact that their interactions were almost entirely antagonistic was irrelevant. Lister later asks Rimmer where the disc which contains Navigation Officer Kristine Kochanski's (C P Grogan) hologram has been hidden so that Lister could go on a date with her, but Rimmer refuses to switch his own disc off to bring back Kochanski for an evening due to the risk that Lister might not turn Rimmer's hologram on again. Holly has the ability to override Rimmer and switch his disc off but cannot do so because Rimmer outranks Lister and he is programmed to prioritise the former's orders over the latter's.

In "Confidence and Paranoia" (1988), Lister believes that the only reason that Rimmer became a part of the love celibacy society was because he could not get a date, and he could never get a date because Rimmer's mother bought all of his casual clothes. Rimmer denies this, pointing out he went to bed with Yvonne McGruder, but Lister says she thought Rimmer was someone else due to her wonky vision from a concussion. Lister, with the help of a solid manifestation of Lister's confidence (played by Craig Ferguson), deduces where Kochanski's personality disc is hidden as well as a means of how the ship can power two holograms at once. Lister is still unable to go on a date with Kochanski, however, as the disc inside Kochanski's box has been swapped with one containing a duplicate of Rimmer.

In "Me²" (1988), Rimmer is shown moving in with his double as better company in the next bunkroom over from Lister. Rimmer's double reveals that all of Rimmer's brothers were academy educated, but he was not. Rimmer claims that this was because his father could not afford it. Rimmer also mentions taking a film course at night school, although he confuses a cartoon showing at the cinema in the episode with Citizen Kane. Lister watches a video of Rimmer's death, where his last words are "gazpacho soup". Demonstrating intense, literal self-hatred, the second cruelly insults and berates the first. Believing that Lister is going to wipe his hologram anyway because of the two Rimmers' constant arguing, Rimmer explained his dying remark as referring to a dinner at the captain's table with six officers, during which he made a faux pas where he had his gazpacho soup taken away to be brought back hot, not realising that gazpacho soup is meant to be served cold. This caused the officers at the table to laugh at him, and he was never invited back. The incident haunted Rimmer for the rest of his life (and beyond). Gradually, his obsession over the incident caused him to remember it as the most disastrous, imbecilic action of his life, and it undermined his self-esteem out of all proportion. Lister, displaying deep empathy, tried to comfort Rimmer, assuring him that "anybody could make a mistake like that." His confession complete, Rimmer prepares to be wiped, but Lister admits that he had already wiped the second Rimmer instead; Lister had allowed Rimmer to believe his "death" was imminent because Lister wanted to know what the "gazpacho soup" remark meant, and he knew that Rimmer would never tell him under any other circumstances.