History and culture
As Remus was a tidally locked planet, the Remans lived on its dark side, and thus were extremely sensitive to light. Some Remans, if not all, possessed telepathic abilities similar to those shown by Vulcans and Betazoids. (Star Trek Nemesis)
Among the Romulan people, Remans have historically been known as great warriors. As such, Romulan senator Vrax employed two Reman bodyguards to intimidate possible opponents. (ENT: "United", "The Aenar")
In 2379, the Remans usurped the power of their Romulan overlords in a military coup, installing their leader, Shinzon (in actuality, a clone of Jean-Luc Picard), as the new Praetor of the Romulan Senate and thus the empire. As an act of war against the Federation, Praetor Shinzon – with his warbird, the Scimitar – then attempted to destroy all life on Earth.
However, with the destruction of the Scimitar at the Battle in the Bassen Rift, after Shinzon's supporters on Romulus turned against him, the bid for Reman superiority was prematurely ended. (Star Trek Nemesis)
Distrust between Remans and Romulans was still prevalent in 2380, when a Romulan guard on Romulus commented to a colleague that he hated Remans, with his colleague commenting Remans were "the worst". (LD: "Veritas")
It has never been established in canon whether the Remans are an offshoot of the Romulans/Vulcans or if they completely separate species or even a cross-breed between Romulans and the original inhabitants of Remus. While certain Reman features, e.g., their telepathic abilities, pointed ears and their forehead patterns, are in agreement with a genetic relation to the Romulans/Vulcans, production sources have consistently referred to them as a "species" distinct from the Romulans (although this might still be interpreted as "sub-species").
When writer John Logan came up with the idea of featuring Remans as the villains of Star Trek Nemesis, he first had to explain to a perplexed Rick Berman and Brent Spiner exactly who the Remans were, that alien race never having been established in canon Star Trek before. Berman and Spiner eventually approved of Logan's idea, giving him the go-ahead to write the species into the upcoming movie. Logan later explained, "Brent and Rick agreed it would be fun to explore the Remans and their relation to the Romulans." (Star Trek Nemesis, pp. xviii & xix)
The Remans were created as a response to the challenge of devising a new, terrifying alien race for Nemesis. "The idea of the Remans being vampirelike slaves, laboring away in the dilithium mines, never seeing the sun, grew out of our desire to create a truly monstrous race," recalled John Logan. "It seemed obvious to me that the Romulans would subjugate some other race to dig dilithium for them. Much too messy for our pristine and elegant Romulans." (Star Trek Nemesis, pp. xviii & xix)
The concept of the Remans looking akin to vampires was also inspired by their lack of exposure to sunlight. "[Director] Stuart Baird and Rick Berman had the idea that they wanted the Remans to have an almost Nosferatulike feeling, but without making them into vampires," remembered makeup supervisor Michael Westmore, referencing the vampire Count Orlok from the 1922 horror movie Nosferatu, eine Symphonie des Grauens. (Star Trek Nemesis, p. 216) Indeed, the script for Star Trek Nemesis described the Remans as having "a disturbing resemblance to the original Nosferatu."  Count Orlok actually served as inspiration for the Reman makeup design. Westmore related, "Stuart [Baird] handed me a picture of Nosferatu and said that was exactly what he wanted. He said, 'I need an alien [species] that looks like this.' And that's exactly what we did. I did some sketches for him and then we went to town on it. We designed the head and ears." (Star Trek Monthly issue 109, p. 32)
The Reman makeup, consisting of foam rubber prosthetics, was ultimately highly elaborate. "It was a full appliance makeup," explained Michael Westmore, "with a complete face piece that blended in with a headpiece. The actors' lower lips and chins were their own; but everything else was covered with the appliances, which were airbrushed with a marbleized pattern [...] We had eight Reman performers, and we didn't know which one Stuart [Baird] was going to pull up front [in closeup], so they all had to have the full makeup, which included teeth and contact lenses and hands painted to match the face." (Cinefex, No. 93, p. 103) The Reman head was sculpted by Earl Ellis. (Cinefex, No. 93, p. 103)
The Remans' ears were made of a semi-translucent latex and included veins. "The ears were neat," commented Michael Westmore. "Stuart [Baird] said, 'I want to be able to see through the ears.' I made the ears out of clear gelatin, so if there's any backlight behind them you can see through them. Then we painted veins on the back of the ears, so if the light was showing through you could even see veining through them." (Star Trek Monthly issue 109, p. 32)
Executive Producer Rick Berman once wondered how the Remans operated the push button controls of their ship with such long, curving fingernails. (audio commentary, Star Trek Nemesis (Special Edition) DVD) The length of the Reman nails actually caused problems during shooting. "No matter how well we glued them on, someone was always popping a nail," recalled Michael Westmore, "so the makeup artists were chasing the performers around with little packs of nails all day." (Cinefex, No. 93, p. 103)
The Reman uniforms were specially painted to appear iridescent, a delicate process that involved several coats. The uniforms were later modified and reused as Xindi-Reptilian uniforms on Star Trek: Enterprise
Ron Perlman, who played the Reman Viceroy in Star Trek Nemesis, enjoyed the fact that the Remans had never previously been viewed by audiences. "We've never seen the Remans, so it's kind of cool to present something that's fresh and uncharted," he said. "A mysterious race." (Star Trek Nemesis, p. 216)
In the final draft script of ENT: "United", Remans were described as having "pallid, bat-like faces." The Remans who appear in that episode (and presumably also "The Aenar") reused masks originally created for Star Trek Nemesis. (Star Trek Magazine issue 120, p. 56) A pair of Reman guards were also included in a deleted scene from "The Aenar". (ENT Season 4 DVD)
In 2015, Remans were included in a list of "Top 50 Alien Species!" which was published by IDW. Commenting on the selection, comics writer Mike Johnson referred to the Remans as "a cool species." ("Top 50 Alien Species!", Star Trek: Ongoing issue #50, "Live Evil, Part 1")
According to the novel trilogy Vulcan's Soul, the Remans were descended from the telepathic Vulcans who refused to give up their abilities during the exodus to Romulus, and were enslaved by the majority non-telepaths who became the Romulans. The Remans were mutated into their current form by exposure to extremophile organisms that lived on the surface of Remus.
The novel Articles of the Federation describes the Remans as being voluntarily transported to an uninhabited Klingon world as a new homeworld a year after Shinzon's death.
In the Star Trek: Titan novel Taking Wing, the newly-appointed Captain Riker is ordered by Admiral Akaar to proceed to Romulus to assist negotiations between the Remans and the Romulans following Shinzon's failed attempt to wage war on the Federation after his assassination of the Romulan Senate. Riker successfully convinced a faction of Remans who had been part of Ambassador Spock's Unificationist group to cease attacks on Romulus in return for the land that they had been attempting to demand from the new Praetor Tal'aura.
The Remans made a brief appearance in the comic book series Star Trek: Countdown, a tie-in to the 2009 Star Trek film. A fleet of Reman ships captured and boarded Nero's mining ship the Narada while it was mining decalithium in the Kimben System at the farthest edge of the Romulan Empire in 2387. The Remans were planning on executing Nero's crew as well as Ambassador Spock, who was on board, before the ship was rescued by the USS Enterprise-E and Captain Data.
In Star Trek Online, which incorporates the story of Countdown, the Remans have colonized Crateris, a failed Romulan colony, with Donatra's blessing. Star Trek Online also shows the Remans as the direct cause of the destruction of Romulus, having intentionally made the Hobus system go supernova under orders from then-Praetor Taris. In the "Cloaked Intentions" feature episode series, a resistance force under the Reman leader Obisek arose to challenge the Tal Shiar's efforts of supremacy over the unstable Romulan Empire, by claiming the secret Romulan factory station known as "the Vault". The Reman resistance would later join with dissident leader D'Tan to settle on "New Romulus", and defend the Vault from Tholian attackers. In the first expansion pack, Legacy of Romulus, the Remans became a playable race under the new Romulan Republic, which also introduced female Remans.