(covers information from several alternate timelines)
Alpha and Beta Quadrants
These aliens were an intelligent species and civilization with advanced technology. Their physical appearance was characterized by a large bald cranium, a large chin and large nostrils and light brown skin. They were dressed in blue leather-like jumpsuits. They had the ability to form links between themselves telepathically, so that they were in continual contact with each other.
Their culture was heavily influenced by the fact that each individual was identical, so that distinctions between themselves were meaningless. Consequently, they did not have leaders or followers. They also did not have a concept of morality.
In 2366, a group of them decided to study the nature of command. To this end, three beings were responsible for kidnapping members of other species which reacted differently to authority. They kidnapped a Human, Captain Jean-Luc Picard, a Mizarian, Kova Tholl, and a Chalnoth, Esoqq. Another being also entered the cell to observe them, taking on the identity of a Bolian Starfleet cadet, Mitena Haro. The cell was designed with tests in mind to give them goals to achieve, and setbacks to deter them when they didn't work together. Meanwhile, the group created replicas of the three individuals to resume their lives and test aspects of command there. For example, Picard's replica gave increasingly strange orders to gauge reaction.
After Picard discovered what happened, they returned him to the USS Enterprise-D since the experiment was then ruined. He trapped the two aliens with him in a force field. They pleaded to be let go. After Picard showed them what it's like to held against one's will, that kidnapping is wrong, he dropped the force field and ordered them off his ship. (TNG: "Allegiance")
A couple of aliens with pointed ears and green spotted sides and foreheads came out of the water.
A bald alien with mottled green skin and a vertical line of small ridges, running across his forehead and chest was working as a waiter at a beach that Deanna Troi and Reginald Barclay both visited in the year 2377. He handed Barclay a tray of two chocolate passion punches that he had ordered. (VOY: "Inside Man")
Bonestell Recreation Facility visitors
Deep Space 9
Deep Space 9 residents
Deep Space 9 visitors
Odo's wanted poster criminals
Several individuals appeared as criminals on wanted posters displayed in Odo's security office on Deep Space 9 from 2369 to around 2372, including Gul Dolak, Praetor Neral, Orta, Plix Tixiplik, Villus Thed, as well as a Ferengi, Klingon and Ktarian criminals.
Buck-toothed alien criminal
This individual was a criminal whose face was displayed on a wanted poster in Odo's security office aboard Deep Space 9 in 2369 through 2372. (DS9: "Vortex", "If Wishes Were Horses", "The Forsaken", "Dramatis Personae", "Duet", "In the Hands of the Prophets", "Crossfire", "Call to Arms", "A Time to Stand", "Rocks and Shoals", "Sacrifice of Angels")
Dessica II visitors
- See: Dessica II visitors
Antwerp Conference attendee
New Zealand alien prisoner
Pink-skinned bald alien
By 2372, members of this species had also traveled to Earth; one female member of this species walked along the streets of San Francisco and came very close to Harry Kim's former apartment. (VOY: "Non Sequitur")
Quantum Café bartender
Harod IV miners
These five alien miners, plus Plix Tixiplik and another Reegrunion miner, were working on Harod IV and were stranded on the planet in late 2368. They were picked up by the USS Enterprise-D and transported to their next destination aboard the ship at the same time as Kamala was transported aboard the ship. When the empathic metamorph entered Ten Forward, she caused quite a stir among the miners because of her beauty. They quickly surrounded her and said suggestive things, to which Data called them rude. For a short time, Kamala adopted the rough personality that appealed to the visiting miners. She egged them on by asking what drink they like. When they replied Aldorian ale, she said that it was her favorite too. Data, who was assigned to be her chaperone, sensed trouble and escorted her out, with the assistance of Worf who intimated the miners.
Two of these aliens were characterized by yellow skin and facial ridges that looked rather similar to Cardassian ridges, and others by brown skin, a number of facial ridges and protrusions and large cheekbones. (TNG: "The Perfect Mate")
Qualor II visitors
- See: Qualor II visitors
Telepathic species trapped in a Tyken's Rift
Their abilities made them capable of broadcasting telepathic messages at a frequency matching that of a Betazoid's REM sleep. This allowed a Betazoid to receive such a message while dreaming, although the communication proved difficult for Betazoids to interpret and was limited by the dreamer's capacity for directed dreaming. In addition, REM sleep in other frequencies was inhibited; this prevented non-Betazoid humanoids in the vicinity from dreaming, which led to debilitating cognitive impairments including irritability, paranoia, hallucinations, and ultimately insanity. The experience could also drive a Betazoid into a profound, but recoverable catatonic state.
The aliens had a knowledge of the Tyken's Rifts phenomenon and of chemistry that was comparable to that of the Federation; they were aware that a large explosion could free a trapped vessel, and they devised a means of generating an explosive chemical reaction for that purpose.
Their contact with the Federation occurred in 2367, when their vessel became trapped in a Tyken's Rift at the same time as the USS Brattain. They attempted to telepathically instruct the Brattain's crew to release hydrogen into the rift, which the aliens wished to use to generate an explosive chemical reaction with a substance they would release. The Brattain could not detect the alien vessel on the other side of the rift, but Andrus Hagan, the Betazoid science adviser on the Brattain, received the aliens' telepathic broadcast while asleep. Unfortunately, Hagan experienced the alien's representation of the hydrogen atom, "one moon circles," as a nightmare and failed to understand it. He became catatonic, while the rest of the crew went insane and killed each other, leaving the Brattain adrift.
Twenty-nine days after the Brittain sent a distress call, the USS Enterprise-D arrived to investigate and became similarly trapped. The ship's counselor, Deanna Troi, was half-Human, half-Betazoid, and also experienced the telepathic broadcast as a nightmare. Troi, a psychologist, and her colleague Beverly Crusher, a medical doctor, detected and monitored the behavioral changes aboard the Enterprise, which led Troi to hypothesize the existence of the aliens after the crew realized that the sleep effects had a cause distinct from the Tyken's Rift. Having used directed dreaming as a therapeutic treatment, Troi offered to attempt to respond to the aliens' message in hopes of coordinating an escape from the rift. Troi and the Enterprise's second officer, Data, then correctly interpreted the message as a request for hydrogen to create an explosion that would free both ships. As the Enterprise began to release hydrogen from its Bussard collectors, Crusher induced REM sleep in Troi, who confirmed receipt of the aliens' message and instructed them to proceed. The individual with whom she was in telepathic contact, previously unseen, then appeared as a bright humanoid silhouette before Troi woke up. An explosion then disrupted the rift, freeing both ships. The alien ship departed in the opposite direction from the Enterprise. (TNG: "Night Terrors")
Utopia Planitia Fleet Yards personnel
- See: Kima's mom
Akritirian maximum security detention facility
Antarian Trans-stellar Rally guests
Avery III prisoner
- See: Unnamed Borg
Unimatrix Zero inhabitants
This individual with bumpy reptilian skin was encountered and assimilated by the Borg prior to 2373. An image this person appeared during one of Seven of Nine's guilt-induced hallucinations after her encounter with a Borg vinculum. (VOY: "Infinite Regress")
This individual with tailhead was encountered and assimilated by the Borg prior to 2373. An image this person appeared during one of Seven of Nine's guilt-induced hallucinations after her encounter with a Borg vinculum. (VOY: "Infinite Regress")
Mikhal bar visitors
These alien bar visitors were present at a lodge at the Mikhal outpost when Captain Kathryn Janeway and a Mikhal traveler, called Nakahn, were engaged in conversation. He was telling the captain an incredible story of one of his travels. Among them were two females and two male aliens. (VOY: "Darkling")
Mokra-controlled planet aliens
These alien species were living on a Mokra-controlled planet in 2372. They visited the marketplace when an away team of the USS Voyager was attacked and imprisoned by soldiers of the Mokra Order. (VOY: "Resistance")
Ord'mirit mining vessel commandant
This individual was the commandant of an Ord'mirit mining vessel encountered by the Silver Blood USS Voyager in orbit of a class Y planet in 2375. He contacted the Voyager and asked them to leave the planet and its orbit immediately. (VOY: "Course: Oblivion")
One was stopped and questioned by Kathryn Janeway who was lost and looking for her work position at the Central Power Facility, he pointed her towards the supervisor's office, and told her "over there". (VOY: "Workforce")
Ridged forehead alien
These aliens had a Human appearance but featured a prominent ridge from the nose up to the forehead. Three members of this species were held as slave workers at the Central Power Facility on Quarra in 2377. (VOY: "Workforce", "Workforce, Part II")
Ridged nose alien
This alien had a Human appearance but featured a prominent ridge on the upper nose part of the face. Two members of this species were held as slave workers at Central Power Facility on Quarra in 2377. (VOY: "Workforce", "Workforce, Part II")
Sobras bar patron
In 2372, Tersa informed Neelix that this dancer had shown him a puzzle he was completely engrossed in. He added that the first man to solve it, and move only two rods to change it from a dodecahedron to an icosahedron, would have the privilege of spending the night with her. Neelix took a seat at Tersa's table and offered to help with the puzzle if the Kazon Jal agreed to listen to him first. (VOY: "Alliances")
Tau's city traders
This alien buyer was attempting to broker a deal with Tau, a leader of pirates who stole technology from various starships. Tau told him he could provide him with all the weapons he needed, even a ceremonial spear. When the buyer said Tau's price was too high, Tau threatened to sell the weapons to the buyer's enemies instead. (VOY: "Concerning Flight")
This alien visitor was invited aboard the USS Voyager to discuss a deal for a warp coil. This was just a ruse, in order to question him concerning stolen Voyager technology. He was in possession of a tricorder, a compression phaser rifle, and was wearing a command division Starfleet uniform. He admitted that he had purchased the items from a man named Tau, a leader of pirates who stole technology from various ships. He did not know where Tau was, as he always dealt with a go between. In return for his information, he was permitted by Commander Chakotay to keep the items he'd acquired, a deal which did not particularly impress him. (VOY: "Concerning Flight")
Commerce planet visitors
Several members of unknown species visited a planet in the Delta Quadrant in 2374 to conduct business. The away team from the USS Voyager questioned some of them about their stolen technology. Additional visitors include a male Rotciv.
The first fighter fought a match against the Hirogen fighter but lost. The second one trained with the female fighter in the quarters. The third alien fighter was present in the quarters when Seven of Nine was forced to comply and when the Hirogen fighter trained her. (VOY: "Tsunkatse")
Another alien was a member of a species with a long face, which was also found in the Alpha Quadrant.
Other unspecified locations
A distress call from this alien starship captain, was received by the crew of the Voyager in 2375. He died along his crew after being trapped in the chaotic space for over one year and experiencing hallucinations. (VOY: "The Fight")
That year, the Voyager crew discovered that the Hirogen had hunted this race, after coming across the eviscerated skin from an individual aboard a derelict vessel. Upon discovering the skin, Seven of Nine pointed out that the Borg found a similar instance done to members of Species 5174. Following The Doctor's autopsy, Janeway requested that the remains be returned to his ship in hopes that "his people may be able to retrieve him." (VOY: "Hunters")
Holographic corner man
Intruder alien's species
This intruder alien launched an unprovoked attack against one of USS Voyager's Class 2 shuttles in 2373, killing Ensign Ahni Jetal and damaging The Doctor's program, which caused a conflict in his programming that couldn't be resolved. Following the attack, The Doctor beamed him back to his ship; Harry Kim, however, thought that The Doctor should have beamed him into space. After his ship exchanged fire with Voyager for a few minutes, he finally withdrew.
This species was reptilian in appearance, with large boney hands and long fingers. Aside from starships, they possessed other such advanced technology as transporters, and directed energy weapons (ship mounted and hand-held). According to Seven of Nine, this species was "unknown to the Borg." (VOY: "Latent Image")