Let's face it: A lot of Star Trek aliens over the years, on The Original Series and later ones, were no more than actors wearing a weird headpiece or a few bumps on their noses. A lot of this came out of creator Gene Roddenberry's invocation of the "parallel worlds" concept, meaning that there were theoretically millions of planets in the galaxy where humanoid life had evolved very closely to that of Earth and even shared some similar historical developments.
Of course, this was mainly a budgetary thing: They only had the money for, say, a frontier town on a planet that resembled the Old West and whose inhabitants had a rather large ridge across their forehead (I'm making that up, but some episodes were not that far off!). But The Original Series, even in those days of little money and relatively crude special effects, managed to pull off a few life forms that were truly alien -- and in some cases, almost beyond the understanding of the crew of the U.S.S. Enterprise.
Here, then, are 15 of the strangest, most exotic and most, er, alien aliens Star Trek ever had trundle or shimmer or coagulate across the screen. I'm not saying that the show pulled all of them off effectively, but they were all at least one hell of a lot odder than a guy wearing just a pair of pointed ears ... oh wait.
15. The salt vampire (from "The Man Trap")
Right in the very first episode ever broadcast (although it was the fifth filmed in regular production), Star Trek introduced one of its more provocative creatures. The last surviving member of an extinct species on Planet M-113, the creature stands more or less like a human, with two arms and two legs, but the hands at the ends of those arms have just three fingers each, all covered with suckers that the creature uses to extract salt from its victims -- salt being the one thing it needs to survive. And how, with its stringy white hair, brownish skin, sagging features and funnel-like snout, does it even get close enough to attack? Easy: it can hypnotize its victims and/or look like anyone they happen to be thinking about.
14. Neural parasites (from "Operation: Annihilate!")
The Enterprise investigates a pattern of mass insanity that seems to be traveling from planet to planet and comes upon the source on the planet Deneva: single-cell organisms that infiltrate human bodies through their spinal cords and take control of their minds. The organisms are part of a single hive mind, as Spock deduces once he himself is infected by a parasite. Creature maker Wah Chang made the things from bags of fake vomit. They're gross and gooey-looking, although in some of the scenes where they fly it's obvious they're being pulled along on wires. Nevertheless, they're still probably the most viscerally disgusting creatures the original series ever showcased, and the idea of them all being part of one large brain is an eerie one.
13. The Companion (from "Metamorphosis")
Kirk, Spock and McCoy discover that the inventor of the warp drive, Zefram Cochrane, is alive and well and has been living for the past 150 years on an otherwise empty planet with a mysterious alien entity that keeps him immortal and permanently 37 years old. They eventually learn that the Companion is female, is in love with Cochrane, and yearns to have a real relationship with him. The Companion was one of several entities on Star Trek that were composed of pure energy or some other non-physical material, usually necessitating an optical effect instead of a costume or oversized prop. But the Companion is probably the most unusual one in that it has a distinct personality, emotions and ability to communicate -- and all it wants is domestic bliss.
12. Sylvia and Korob (from "Catspaw")
These two alien wizards appear in human form for most of this Halloween-themed episode, which finds Kirk, Spock, Scotty, Bones and Sulu trapped in a macabre maze of witches, castles, black cats and spells by these two visitors from another galaxy. In the end, once their source of power (the "transmuter") is destroyed, Sylvia and Korob are revealed in their true form: small, ornithoid lifeforms that were made of pipe cleaners, some blue fluff, crab pincers and other materials. Sadly the strings that held the puppets up are clearly seen in the original episode (although erased in the remastered version), rendering them kind of silly. More intriguing is their allusion to serving the "Old Ones," a reference also made by the android Ruk in "What Are Little Girls Made Of?" Both episodes were penned by horror writer and Lovecraft acolyte Robert Bloch.
11. The vampire cloud (from "Obsession")
Another one of Star Trek's cloud-like monsters figures in this episode, one of the best of the second season. When a landing party is attacked and drained of their blood by a mysterious cloud, Kirk realizes that it may be the same creature that attacked his previous ship, the Farragut, on which he was a lieutenant; for 11 years he's harbored guilt over the death of the captain and many of the crew because he delayed firing on the thing. It's the show's second variation on Moby Dick (after "The Doomsday Machine"), with Kirk in the Ahab role this time. But the story works and the creature itself is surprisingly effective, if only because of its single-mindedness and rudimentary, malevolent intelligence.
10. Balok (from "The Corbomite Maneuver")
This commander from the "First Federation" is the closest to a traditional human form on this list, but we had to include him because the revelation of his true form has always struck us as so surreal and outright bizarre. When the Enterprise first encounters Balok's intimidating vessel, the massive Fesarius, they pick up an image of Balok that resembles a leering goblin. But that turns out to be a fright-mask meant to deceive the crew; Balok turns out to be a small, bald, child-like humanoid with a deep voice and a penchant for a drink called tranya. Played by seven-year-old Clint Howard in a bald cap and heavy eyebrows (with his voice dubbed), Balok comes across as even more eccentric that other humanoid guest aliens like the Andorians and the Tellarites. Fun fact: one actor considered for the part was Michael Dunn, who later played Alexander in "Plato's Stepchildren."
9. The Providers (from "The Gamesters of Triskelion")
Kirk, Chekov and Uhura are transported to a planet called Triskelion where they must compete in a series of gladiatorial games in order to survive; the games are operated and wagered on by unseen masters called the Providers. When Kirk eventually confronts them, they turn out to be three disembodied brains that control a vast underground complex and spend all their time betting on the games and collecting more slaves ("Thralls") for their amusement. Like the Organians of "Errand of Mercy," the Providers (the real name of their species is never disclosed) have evolved beyond the need for physical bodies, although they have not progressed like the former race into the realm of pure energy. And also unlike the Organians, the Providers are arrogant, haughty and quite interested in themselves and their own needs. For a trio of brains, they are no brainiacs.
8. The Beta XII-A entity (from "Day of the Dove")
This being comprised of pure energy also has one hell of a diet: unlike the vampire of "Obsession" which feeds off human blood, this thing (which resembled a cluster of rotating lights that turn red when fully "charged") subsists on violent emotions like hate and anger. So naturally, throwing a bunch of Klingons onto the Enterprise, arming both sides with medieval weapons and stoking the fires of suspicion and hostility would end up becoming a never-ending buffet for this creature. That's what happens in this popular third season episode, although Kirk and the Klingon commander Kang (Michael Ansara) eventually find a way to laugh the whole incident off and send the weakened entity dejectedly out into space, where it winks out of existence. This fellow could also be kissing cousins with the fear-hungry "Red Jack" entity from Season 2's "Wolf in the Fold."
7. The Zetarians (from "The Lights of Zetar")
The last of our non-corporeal aliens were in the first Star Trek episode I ever saw, and they scared the hell out of me: in one scene, this disembodied group of survivors from the planet Zetar enter a woman's body at the Memory Alpha space library and turn her all kinds of sickly colors while weird gurgling noises emerge from her throat. The Zetarians -- the last one hundred of them from their devastated planet -- are looking for a host whose body they can call home, but they're pretty arrogant and invasive in the way they go about it so it's into the decompression chamber with them. By the time this episode ran late in Season 3, fans had already seen plenty of twinkling energy beings, but it's what happens when when the Zetarians possess someone that makes them still memorable.
6. The Melkot (from "Spectre of the Gun")
Interestingly, the third season of Star Trek had perhaps the highest number of non-humanoid aliens, and the first show filmed that year set the tone with this xenophobic race. When the Enterprise is rebuffed in its attempts to make contact with the Melkotians, Kirk and a landing party beam down to their planet anyway, where their punishment is Death by Western B-Movie. The Melkot that presides over this appears out of the planet's misty atmosphere looking like a big, round, floating boulder with large glowing eyes and no other distinguishable features. As usual, Kirk teaches the Melkot a lesson or two before the show is over and diplomatic relations are opened, although sadly we never ran into the Melkotians again.
5. Yarnek (from "The Savage Curtain")
Yarnek was a member of a race called the Excalbians, who were interested in studying the differences between the concepts of "good" and "evil" by pitting representatives of both against each other. That's the basis of this late Season 3 segment, which lines up Kirk, Spock, Abraham Lincoln and Vulcan philosopher Surak against a quartet of real baddies from galactic history. Yarnek itself was played by famous monster maker Janos Prohaska, who shoved inside a number of suits for Trek and other shows like The Outer Limits; as envisioned in this episode, the Excalbians come from a planet made of molten lava and their body temperature is appropriately unpleasant, as Kirk finds out the hard way. "Like living rock with heavy fore-claws" is how Yarnek and his race are described, and his promise to stage more such events in the future hints at a rock-like stubbornness as well.
4. Kollos (from "Is There In Truth No Beauty?")
Kollos is an ambassador from a race known as the Medusans, who are capable of brilliant and sublime thoughts but whose form can drive humans insane with its ugliness. He travels in a special container that only can be opened in the presence of certain people who wear a special visor; even then it's dangerous to glance directly upon him. The Medusans are enlightened, peaceful and compassionate beings; that their appearance is so destructive to those who see them only reinforces the story's themes that such appearances can be deceiving. Facing the difficult task of showing even brief glimpses of a being so hideous-looking, the show's special effects team settled for intense flashes of light and color. They didn't drive viewers insane, but may have given them a headache.
3. The Gorn (from "Arena")
Bipedal and recognizably shaped like humanoids, the Gorn are nevertheless very far from anything resembling humans; instead they look like crocodiles that walk on two legs. These slithering, vicious, reptilian beings are represented by the commander of a ship that has destroyed a Federation outpost and then engages in battle with the Enterprise, until a superior race called the Metrons beam the Gorn captain and Kirk to an asteroid where they will settle their differences in person. One of the best-remembered and popular aliens from The Original Series, the Gorn later showed up in episodes of Star Trek: The Animated Series and Star Trek: Enterprise (in the mirror universe), but none of the series have ever fully explored the nature of the species or their government, known as the Gorn Hegemony (they've made small appearances in some scattered Star Trek novels).
2. Commander Loskene (from "The Tholian Web")
The Tholians are known for their punctuality, their xenophobia and their territorial nature, as we learn in the third season TOS episode that first introduced their eerie race of strange crystalline beings. They're quite adept at space flight and have some very unconventional weapons, including the energy field of the title. They don't resemble anything humanoid, with their angled bodies, glowing eyes and apparently extremely high temperatures, and outside of their first appearance on The Original Series, the Federation has skirmished with them in episodes of The Next Generation, Deep Space Nine and Enterprise. The Tholians always seemed like a menace that was waiting to really wreak havoc with Starfleet...perhaps on Star Trek: Discovery?
1. The Horta (from "The Devil in the Dark")
While Yarnek from "The Savage Curtain" was sort of like living rock, the Horta from the planet Janus VI comes even closer -- an utterly alien form of life made of silicon and a kind of fibrous asbestos. Creature creator Janos Prohaska reportedly crawled into producer Gene Coon's office one day wearing a Horta costume, prompting Coon to say he'd write a script around it; the result was one of Star Trek's all-time classics, as the monstrous-looking and quite deadly Horta turns out to be a mom just protecting her vast trove of eggs from destruction by human miners. It's a quintessential example of what makes Star Trek so enduring: one of the show's most bizarre and gruesome-looking aliens turns out to be one of the most humane, peaceful and empathetic characters ever introduced on the show.