Like the infinite galaxy, it seems like there will be no end to Star Trek’s popularity. The Original Series introduced the world to Gene Roddenberry’s inclusive vision of the universe, but it didn’t mean that Captain Kirk and Starfleet didn’t have foes to fight. The franchise introduced numerous species that had a fearsome reputation in the galaxy. Since The Original Series, Star Trek has widened its reach with the Star Trek: The Next Generation TV programs and films.

Star Trek: Deep Space Nine explored what the Starfleet is like when the scope is limited to a space station, while Star Trek: Voyager explored the Delta Quadrant. Star Trek: Enterprise focused on a pre-Kirk world as a prequel to The Original Series. Since Abrams has been given the keys to the series, shows like Discovery and Picard have been released. Although Starfleet has both military and diplomatic duties, their missions often revolve around exploring new worlds. Sometimes the crews come across new allies, but they also make new enemies.

Updated December 23, 2023 by Joshua M. Patton: For nearly 60 years, Star Trek has been the blueprint for the ongoing sci-fi saga, even inspiring Doctor Who, the one series older than it. Gene roddenberry created this universe as a vehicle for his humanist, progressive vision of what humanity could be. The starship Enterprise was meant to represent the starship Earth, but there is a whole wide universe out there to explore. Whether serving alongside humans, like Spock or Worf, or meeting them on their journey, the alien races in Star Trek represent everything else. Some are benevolent and kind, while others are cruel, violent and backwards.

30 Tribbles

Tribbles at a Glance

Though they may be cute and cuddly in appearance, the now legendary Tribbles are a huge threat to any planet they find themselves on. They are an invasive species that require very little to food to function and, critically, to multiply. They reproduce at an unbelievable rate and consume everything in the area in short order when they reach a critical mass of numbers.

Sure, they aren't a species with grand machinations and nefarious designs but they could be genuinely devastating in the right circumstances. They are adorable though, losing them some power points here.

29 The Moopsy

Moopsy at a Glance

Introduced in Season of Star Trek: Lower Decks the Moopsy is a non-sentient species found in one of the universe's ubiquitous menageries of dangerous creatures. The adorable round creature has a cute face and an even sweeter voice, which it uses to say only "Moopsy." However, it's one of the most dangerous creatures the crew of the USS Cerritos ever encountered. Because while the Moopsy is precious, it lives only to drink bones.

The important question isn't "How does something drink bones?" The question fans and Starfleet officers should be asking is how does one stop such a creature. Luckily, Lieutenant Mariner and Commander Ransom use the latter's teeth to lead the creature back to its enclosure. But there are more moopsies out there, and a galaxy's worth of bones ripe for the drinking.

28 The Gorn

The Gorn at a Glance

Though their initial appearance has been rendered less frightening thanks to some fairly comical physical effects, the Gorn have got a long going for them. They are said to be extremely physically strong (despite Kirk holding his own the first time he faced them) and they also have a superior intellect, with confirmation that they were at least capable enough to produce warp drives.

They aren't preoccupied with taking these abilities far beyond their own world, instead content to stay and endeavor to help their own society to flourish. That said, they are fiercely territorial and would put up a good fight against most of the other species in the wider Star Trek universe.

27 The Xindi

The Xindi At a Glance

The Xindi are a single species, but one that evolved into five separate races: Apes (humanoid), Arboreals, Insectoids, Reptilians and Aquatics. Their backstory is an interesting one, as they were forced to flee their original homeworld when it was rendered uninhabitable following a war between the Xindi-Insectoid and Xindi-Reptilian peoples. The war caused the extinction of a sixth race: the Avians.

They were guided to new worlds by an extradimensional race called Sphere Builders. They constructed one of the most destructive weapons in the galaxy, attacking Earth with it. They were an early and very significant threat to the Federation, but Captain Archer and the NX-01 Enterprise crew formed an alliance with them and sent the Sphere Builders back to their own dimension.

26 The Tholians

Tholians at a Glance

The Tholians are one of the more bizarre creatures out there in space, an insectoid species made of non-organic and crystalline structures that form a near-impenetrable mineral carapace. They live in extremely hot environments (around 404 Farenheit) and, though they could tolerate lower temperatures for a time, it would kill them in relatively short order.

As with many bugs on Earth, Tholians communicate via a series of clicks and other sounds. They are also a species with strict values related to punctuality and they are not afraid of conflict in any sense. Though most famous for their interactions with both the Defiant and Enterprise, they have long had predominantly antagonistic dealings with the Federation.

25 The Hirogen

Hirogen At a Glance

The fact that the Hirogen had essentially managed to secure their position as the dominant species across a swath of the Delta Quadrant in the 24th century is testament enough to their broad skillset. Their entire culture centers on hunting other alien races that they feel are worthy of taking on in battle and defeating them to further their own honor.

They are very large in stature and wear armor of their own design, notorious for its significant protective properties. Equally, their ships are very advanced and quick to travel across vast distances, meaning they were able to make significant military progress over a short period. They menaced the USS Voyager a number of times, even after Captain Janeway gave them holodeck technology to hunt without harming people.

24 The Nausicaans

The Nausicaans at a Glance

Most species like to play darts with a board, but the Nausicaans prefer to toss them at each other. Large, muscular, and generally physically imposing, this species has gained a considerable reputation. Their main vocations include mercenary work, bodyguard duties, and even piracy. They're often the choice of hired help for species such as the Ferengi.

Before he became captain, a young Jean-Luc Picard discovered the terrifying outcome of a simple fistfight with some drunken Nausicaans. During the brawl, one of them rushed from behind and pierced his heart with a blade. Luckily, he was able to survive with an artificial heart.

23 The Romulans

Romulans at a Glance

The Romulans’ first appearance was in Star Trek: The Original Series in 1966. Since then, they have also been in several of the subsequent Star Trek series, as well as numerous films. The Romulans and the Federation have had a complicated relationship over the years.

Romulans are the opposite of Vulcans — instead of being unfeeling, they feel everything and act on their rage. The Romulans have a strong military force to back up any actions they may take against the Federation or other planets. This species also has a penchant for conquering other races, which is something the Federation has had to fight against.

22 The Letheans

The Letheans at a Glance

This telepathic species is dangerous both from a physical and psychological standpoint. The Letheans managed to wipe out the entire Gretharan civilization in a bloody war. Since then, they've largely been relegated to mercenary work.

Dr. Julian Bashir had a deadly encounter with a Lethean named Altovar, who attempted to get his hands on a dangerous substance known as bio-mimetic gel. While under Altovar's mercy, the good doctor was forced to confront his inner psychological baggage. One Lethean even managed to fall to Kor's blade during a fight for the Sword of Kahless.

21 The Klingons

Klingons at a Glance

Klingons are a classic Star Trek species and for good reason. They are a fascinating warrior species and have several ceremonies and customs revolving around fighting and honor. Klingon military strength combined with their traditional values have made them a worthy opponent in the Star Trek universe. Created by Gene L. Coon as part of an anti-war allegory, they've evolved beyond antagonists to (sometimes) allies of the Federation. Following a 23rd century war with the Federation (both hot and cold), the Klingons would have a presence in Starfleet.

Lieutenant Commander Worf is probably the most famous Klingon to serve in Starfleet, but there’s also B’Elanna Torres, a half-Klingon who served as U.S.S. Voyager’s chief engineer. That said, the notorious Klingon temper is still something that needs to be managed. They signed a peace agreement called the Khitomer Accords with the Federation after Captains Kirk and Spock uncovered a conspiracy of both Klingons and renegade Starfleet officers, ironically proving the two groups could work together. But Klingons are always one cross word away from a glorious battle.

20 The Cardassians

Cardassians at a Glance

The Cardassians’ first episode in the Star Trek universe was in Star Trek: The Next Generation. This alien species gave the Enterprise-D crew a formidable enemy, and even characters on Deep Space 9 and Voyager have spoken of the power of the Cardassians. Odo from Deep Space 9 even said that the Cardassian intelligence organization is more unforgiving than the Romulan one (which is saying a lot).

The Deep Space 9 crew had multiple interactions with the Cardassian character Gul Dukat, who has treated Captain Sisko as both an ally and an enemy. Even the Voyager crew was affected by the Cardassians — the only reason the Maquis were present on Voyager in the first place was a treaty between the Cardassians and the Federation.

19 The Medusans

Medusans at a Glance

Introduced in the third season of The Original Series, the Medusans were described as so hideous they drove humans (and most other sentient species) mad from the mere sight of them. Vulcans, like Spock, could view them while wearing protective eyewear. They were a peaceful and kind race, interested in exploration and connection, despite the risk their appearance presented.

On Star Trek: Prodigy, now on Netflix, member of the crew, Zero, is a Medusan who was captured and imprisoned on a far-off planet. Zero, who is agender, built a mechanical suit to surround their form and allow them to exist with an interact with the crew. Highly intelligent and skilled, Zero is one of the most important members of the USS Protostar crew.

18 The Metrons

Metrons at a Glance

Introduced in the same episode as the Gorn, the Metrons were an advanced species far beyond the capabilities of Starfleet and the USS Enterprise. They were able to stop the Gorn ship and the Enterprise in space when they sensed Kirk's intention to harm the Gorn ship who'd attacked their colony. They ordered Kirk and the Gorn captain to fight to the death, the penalty the destruction of the losing vessel. So, they're not that advanced. Kirk's capacity for mercy impressed them.

An ancient and long-lived species, not much is known about the Metrons. After sending the Enterprise on its way, they told Kirk they might be interested in a second contact in 1,000 years or, coincidentally, around the time Star Trek: Discovery's later seasons unfold.

17 The Vulcans

Vulcans at a Glance

It is impossible to imagine the Star Trek universe without the Vulcans. The Vulcans have been a presence in Star Trek since the first, failed pilot for The Original Series, and continue to play a critical role in Star: Trek Discovery. What makes the Vulcans so formidable is their ability to act only on logic and reason instead of emotions.

Vulcan physiology also allows them to stay in dangerous environments slightly longer than humans, as seen in Spock’s sacrifice in The Wrath of Khan. Other reasons why the Vulcans are so powerful are their ability to mind-meld, as well as their physical strength and fast reflexes.

16 Androids and Synthetic Lifeforms

Androids/Synthetics At A Glance

While androids such as Data were previously regarded as little more than property by the Federation, a landmark court case changed all of that. Thanks to the guidance of Guinan, Captain Picard was able to convince the court that Data was part of a sentient species and deserving of all the rights and privileges that come with that designation.This extended to all his fellow "synthetics" in the first season of Star Trek: Picard.

However, Data isn't the only synthetic lifeform in the universe. There are many sentient computers across franchise history, as well as the ExoComp species introduced on Star Trek: TNG. Similarly, self-aware holograms are another form of life, including Vic Fontaine from Deep Space Nine and the Doctor from Voyager. In fact, the latter character was also part of a court case. It didn't establish his personhood, but it did give him and other holograms some rights. There is debate both in the narrative and the fandom about which beings are, actually, "alive."

15 Human Beings

Everyone is an alien to someone, including human beings. Sure, humans are the only species on this list known to exist, but Star Trek has often shown how alien they can be to both other species and humanity as it exists in the 20th and 21st centuries. Perhaps what makes human beings so powerful is the rapid advancement they made since 2063 when Vulcans first landed on Earth and introduced themselves. Earth is a paradise in the Star Trek future. No crime, no hunger, no illteracy and, perhaps most baffling, no money. The humans in this universe are a constant reminder of the potential real-world humans could reach if we just looked up.

Of course, humans are also no joke to the universe at large. Enterprise showed how integral humanity was to forming the United Federation of Planets, bringing peace to quarreling species like the Vulcans and Andorians. Every other series shows how humanity is capable of meeting and, when needed, defeating any challenge. However, humans are at their most heroic when not fighting but, instead, trying to learn and understand those different from them.

14 The Jem'Hadar

The Jem'Hadar At a Glance

The Jem'Hadar were a replitician species genetically-engineered to be the "warrior species" bred only to serve the Dominion. They don't fear death or require sleep. They are short-lived but grow quickly, so their numbers don't dwindle, making them one of the Federation's most dangerous foes. To ensure their loyalty, the Jem'Hadar are controlled with an addiction to a drug known as Ketracel-White.

This substance serves as a reward for their obedience, while insubordination results in their immediate death. Nobody showcases the ethos of the Jem'Hadar better than First Omet'iklan's speech, which goes "I am dead. As of this moment, we are all dead. We go into battle to reclaim our lives. This we do gladly, for we are Jem'Hadar." After the end of the Dominion War, the Jem'Hadar haven't been seen in the Star Trek universe.

13 The Ba'ul

The Ba'ul at a Glance

The Ba'ul were a very creepy aquatic, semi-humanoid species introduced in the second season of Star Trek: Discovery. In the 22nd Century they took to the stars and subjugated the Kelpian race, who believed they were a "prey species." In fact, the Ba'ul were prey for Kelpians after they went through a change where they lost their "fear ganglia." Commander Saru of the USS Discovery freed the Kelpian people from their control.

When the Discovery jumped 1000 years into the future at the end of its second season, Saru learned that Kelpians and the Ba'ul shared their homeworld, Kaminar, in a peaceful, symbiotic relationship. The Ba'ul are an aquatic species, able to emerge for a short time, but appear covered in a thick, viscous black goo.

12 The Changelings or 'the Founders' of the Dominion

The Founders at a Glance

Changelings are shapeshifters, the most prominent one being Odo from Star Trek: Deep Space 9. Changelings aren’t limited to just humanoid forms in terms of their metamorphosis. They can transform into inanimate objects, animals, starships and even fire. The Changelings’ weakness, however, is that they need time to regenerate in their natural liquid state.

Although Odo allied himself with Starfleet, his species were “the Founders” of the Dominion, a group that wanted to bring “order” to the universe by taking over everything. Changelings think as a collective and are difficult to kill. They were, therefore, a difficult adversary. Starfleet introduced a virus that killed the creatures, infecting even Odo, but Dr. Julian Bashir developed a cure. Changelings captured and experimented on by Starfleet's black ops division Section 31, helped the Borg secretly invade the Federation in Star Trek: Picard Season 3.

11 The Vau N'Akat

The Vau N'Akat at a Glance

Introduced in Star Trek: Prodigy, the Vau N'Akat are a species who first encountered Starfleet when Captain Chakotay and the USS Protostar were lost in time. The arrival of aliens sent the civilization into a downfall, leading to a civil war that decimated their people. The Diviner and the Vindicator, two surviving military leaders, were sent back in time to destroy Starfleet before they could contact them. While their temporal mechanics aren't exactly sound, they are an advanced race with powerful technology.

Along with the villains, Gwyndala of the Protostar crew is the daughter of the Diviner. She understands the good Starfleet does and hopes to save her people. The Vau N'Akat had some space travel capabilities, as well as the ability to travel one-way through time. They created a device that would destroy Starfleet via its communications network the crew couldn't disarm. Both the Diviner and Vindicator traveled with an advanced sentient robot called "Dreadnok."