There are near countless races of humanoid (and not so humanoid) extraterrestrial beings depicted in the Star Trek series. Some are benign and helpful, joining with the United Federation of Planets in their pursuit to bring peace and harmony to the universe. However, others oppose the Federation's aims—seeking to destroy and conquer all that lies in their path. Below are the ten most dangerous races Starfleet has tussled with.
10 The Breen Confederacy
The Breen Confederacy was mentioned on numerous Star Trek series but didn’t appear until Deep Space Nine. A mysterious race with warlike tendencies, not very much is known about The Breen, who wear fully sealed refrigeration suits that obscure their physical from the outside world. In their most bloodthirsty moment, they allied with The Dominion to wage war against the Federation, the Klingons, and the Romulans, destroying Starfleet headquarters on Earth.
9 The Vidiian Sodality
One of the strangest and most repulsive species in all of Star Trek, they first appeared in Voyager and haven’t shown up much since. Suffering from a nasty, flesh-eating disease, the Vidiians amputate and graft body parts from other races onto their crumbling bodies.
Aside from their brutal, patchwork visages, Vidiians are frightening because they view all other races as spare parts--mere resources to be mined from--carving up victims to use their bodies to save their own species and disregarding their right to life.
Though not the most overtly threatening Star Trek race, Changelings are tough to kill, function as a hivemind, and have unmatched shapeshifting abilities, making them formidable adversaries. They do have a weakness in that they must return to their natural, liquid state in order to recuperate and regenerate. The most famous Changeling in the Star Trek universe is Odo from Deep Space 9. Though he became an ally of Starfleet, many of his race were part of The Dominion, a group that sought to bring order to the universe through terror and domination.
Once a race of high-minded, cultured individuals, the Cardassians were forced to become brutal and militaristic to survive. They first appeared in The Next Generation, though they’ve been spoken about in Deep Space 9 and Voyager as being even more dangerous (supposedly) than iconic baddies, the Romulans. A clever and crafty race, the prejudiced attitude with which they regard other species and their totalitarian ways lead them to infamously conquer the planet of Bajor, an event which reverberates throughout the entire Star Trek universe.
Evil with a capital “E”, the Pah-Wraiths are the non-corporeal, eternal enemies of Bajoran prophets. According to Bajoran lore, the Pah-Wraiths are themselves excommunicated prophets who formed a cult to combat the Cardassian Occupation of their planet.
Though they physically resemble other prophets, they boast devastating fire abilities and can induce hallucinations in their enemies. They are also able to possess the bodies of others, as they did in Deep Space 9 when they resurrected the Cardassian Gul Dukat in an attempt to destroy the known universe.
The series' OG antagonists, the Romulans first appeared way back during the show's first season in 1966. Ever since, they’ve been a thorn in the sides of every captain from Kirk to Janeway and beyond. The polar opposite of the unfeeling, logical Vulcan race, Romulans are full of wrath and make knee-jerk decisions. The Federation has a complicated relationship with the cunning, militaristic race, and has had to tamp down their attempts to conquer other species wholesale time and again.
The Klingons were initially less prominent than the Romulans in Star Trek, but quickly subsumed them in popularity as the years progressed. A proud warrior species with deeply held beliefs, customs, and ceremonies tied to battle and honor, they began as antagonists before becoming members of the Federation in The Next Generation.
Lieutenant Commander Worf became the most famous Klingon to ever serve in Starfleet, and though The Federation occasionally continues to butt heads with Klingon factions, they believe it better to have them as close friends than enemies.
3 The Borg
Perhaps the greatest and most recognizable of the more modern Star Trek villains, The Borg were instantly iconic when they first appeared on The Next Generation. A robotic humanoid race that grows its numbers by “assimilating” other species, The Borg are one of the most unsettling in the Star Trek universe. Their ability to tamp down individuality and absorb others into their collective brain makes them feared across galaxies, and they are one of the few races who actually succeeded in besting a Starfleet Commander when they successfully assimilated Captain Picard, albeit if only briefly.
Interestingly, later in the series, it was revealed that The Borg are able to return to their human state and reverse their assimilation. Voyager’s Seven of Nine was one such example and was a valuable asset to her crew due to the unequaled level of knowledge she attained as a member of the species.
2 Species 8472
The only entity capable of striking fear into The Borg, Species 8472 is so formidable that it once forced a temporary alliance between Starfleet and The Borg in Voyager. Known only by the species serial number given them by The Borg, the creatures have an extremely hardy genetic makeup that makes them immune to assimilation, inspiring in the Borg (who view them as a genetically perfect species) both extreme admiration and terror
Species 8472 possesses biotech beyond what both Starfleet and The Borg could imagine, and for reasons unknown, they seek to wipe out all life in the galaxy. The only option available to the Voyager crew and their Borg allies was to use nanoprobes in a warhead to beat them back.
One of Star Trek’s most popular (and occasionally irritating) characters, Q is a member of an unknown, time-traveling species that frequently toys with the Starfleet Crews. Though he appears to Starfleet in human form, it is unknown what he truly looks like (or whether “he” is a he at all) and his motives are often shadowy and unclear. What is clear, is that he is likely one of the Universe’s most powerful beings, able to alter the fabric of reality and go anywhere he chooses with a snap of his fingers.