This page contains information regarding Star Trek: Lower Decks, and thus may contain spoilers.
The Nausicaans were a humanoid species from the Beta Quadrant. Their homeworld was Nausicaa. (TNG: "Tapestry"; ENT: "Fortunate Son") They occupied a region of space located in the Alpha Quadrant. (VOY: "Q2")
Nausicaans were typically observed to have a large and muscular physique, generally surpassing two meters in height, with great physical strength. Their faces were commonly ashen in color and were distinguished by a prominent bone structure, with sharp tusks protruding at either side of their mouths. Some Nausicaans also had a line of four small horns that ran vertically down the forehead. (TNG: "Tapestry"; ENT: "Fortunate Son", "Canamar", et al.) At least some individuals had eyes with black sclera and yellow irises, the latter of which glowed red when they were angered. (LD: "We'll Always Have Tom Paris")
In the year 2151, Starfleet made first official contact with the Nausicaans when the Earth starship Enterprise NX-01 intervened in a conflict involving the ECS Fortunate and a force of Nausicaan pirates. (ENT: "Fortunate Son")
In the mid-2320s during his sophomore year, Cadet Jean-Luc Picard was assigned to training on Morikin VII where he had his first encounter with Nausicaans, who had an outpost on a nearby asteroid. (TNG: "Tapestry")
In 2327, the newly graduated Picard and two of his friends, Cortan Zweller and Marta Batanides, became involved in a fight at the Bonestell Recreation Facility on Starbase Earhart after a trio of Nausicaans cheated during a game of dom-jot. During a melee, one of the Nausicaans stabbed Picard through the heart with a Nausicaan sword, severely injuring him and necessitating the implanting of an artificial heart. (TNG: "Samaritan Snare", "Tapestry")
A Nausicaan was seen in a bar on Dessica II in 2370 while the senior staff of the USS Enterprise-D was searching for clues about the whereabouts of Captain Jean-Luc Picard in that establishment. (TNG: "Gambit, Part I")
Nausicaans were a common choice as bodyguards or mercenaries – FCA liquidator Brunt used two Nausicaans as bodyguards in 2372, when he investigated a labor union set up by employees of Quark. The Nausicaans severely beat Quark in an unsuccessful attempt to force Rom to shut down the union. (DS9: "Bar Association")
In 2374, Quark proposed using Nausicaans to break his brother out of his holding cell on Terok Nor. For five bars of gold-pressed latinum, Quark could hire five Nausicaans, a fast ship, and very few questions. Breaking Rom out of the holding cell would have been child's play compared to the things Nausicaans are used to doing. (DS9: "Favor the Bold") When discussing how to rescue Ishka from the Dominion, Rom suggested to gather the toughest mercenaries available, including Nausicaans, Breen and Klingons. (DS9: "The Magnificent Ferengi") Later that year, Quark made 200 bars of gold-pressed latinum by selling Denevan crystals to a Nausicaan entrepreneur. (DS9: "The Sound of Her Voice")
A Nausicaan representative was part of the holographic diplomacy scenario 12-alpha aboard the USS Voyager, in which Q Junior was to act as a mediator. Here, amongst other species, Nausicaans and Bolians were fighting over the mining rights to a dilithium-rich planetoid. The holographic Nausicaan claimed that the planetoid was within Nausicaan space and warned that they would attack anyone who came near it. (VOY: "Q2")
When he was attending Starfleet Academy, Brad Boimler had a run-in with a group of Nausicaans who wanted to eat his heart. His friend Fletcher was able to talk them down to spitting in Boimler's face instead. (LD: "Terminal Provocations")
Technology and culture
During the mid-22nd century, Nausicaans committed acts of piracy against freighters in the same sector for several years. Hunting parties of several warp-capable starships, armed with plasma cannons and protected by shields, worked out of Nausicaan cargo stations. The pirate crews were armed with hand-held directed energy weapons. (ENT: "Fortunate Son")
- See: Unnamed Nausicaans
There were at least two pronunciations of this species' name. One pronunciation, from the script for "Samaritan Snare", was "NAW-sik-can".  The other pronunciation, from the script for "Bar Association", was "NAW-si-can". 
According to the Star Trek Encyclopedia (4th ed., vol. 2, p. 68), this species was "named for the Greek princess of the wind, as well as for the 1984 animated fantasy film Nausicaa." Coincidentally, Patrick Stewart later lent his voice talent to an English redubbing of that anime film, in 2005.
In the final draft script of "Tapestry", this species was introduced with the description, "The Nausicaans are large, burly with hideous features."  The Nausicaan makeup consisted of a facial mask which was painted virtually the same color as bones. (Star Trek: Aliens & Artifacts, p. 120)
In the audio commentary for "Tapestry", Denise Okuda erroneously told Ronald D. Moore that a Nausicaan appeared before that episode, in the installment "Allegiance"; she was likely thinking of the Chalnoth instead, due to the similarities in their physical appearance. As the commentary proceeded, Okuda referred to the Nausicaans as "great" and agreed with Moore that the Nausicaan mouth appliance looks especially good.
The depictions of Nausicaans as thugs and enforcers on Star Trek: Deep Space Nine was partly due to their introduction in "Tapestry", as it was considered effective, and because they had considerably striking makeup. (Star Trek: Aliens & Artifacts, p. 120)
In "The Magnificent Ferengi", the Nausicaans were originally to have captured Grand Nagus Zek and held him prisoner. (Cinefantastique, Vol. 29, Nos. 6/7, p. 55) Ira Steven Behr commented, months before that, "We'll do a show about [the Nausicaans] being an enemy for an episode." (Star Trek Monthly issue 30) Zek's captor was instead ultimately changed to being the Dominion.
In the stage directions from the script of "Fortunate Son", the Nausicaans were described as "tall with crab-like mandibles and a bad attitude." In an ultimately unused line of dialogue from the first draft of that script, Travis Mayweather commented Nausicaans were "the last people you want to meet out here." They were referred to as "a nasty-looking species" in the script of "Canamar", which also noted they had last been depicted in "Fortunate Son".
Nausicaans appear as enemies in the video game Star Trek: The Next Generation - Klingon Honor Guard, where they are called "Nausicans".
In Star Trek Online, Nausicaans are a playable species for the Klingon faction. The Nausicaans were mercenaries allied with the Gorn during the Klingon-Gorn War and when the Gorn surrendered, the Naussicaans did too, becoming formal allies with the Klingon Empire. A few episodes in the game feature the Nausicaans as the player's opponents.