During the Enterprise’s five-year mission in the original Star Trek, the crew encountered many previously undiscovered alien lifeforms — some of them friendly, others hostile and horrifying. While Kirk would almost always try to establish peaceful contact with any intelligent life the Enterprise encountered, it just wasn’t always possible. Here are 10 of the scariest aliens in Star Trek: The Original Series.
10. The Tholians
The Tholians are a species whose bodies consist primarily of orange crystals. Though they are not entirely unreasonable and are open to dialogue with the Enterprise crew, they are ruthless, and eventually deploy the famous “Tholian Web” — a cunning trap which entombs enemy starships inside a vast network of energy beams, immobilising them.
9. Apollo
Apollo literally snatches the Enterprise out of space and forces the crew down to his planet. They learn that this alien was the actual Apollo worshipped by the ancient Greeks. Seeing humans as his children, Apollo yearns to return to the days of his first visit to Earth, and commands the crew to “gather laurel leaves, light the ancient fires, kill a deer, and make your sacrifices to me. Apollo has spoken!” But he soon discovers that humans from the 23rd century are less impressed by him than the shepherds of two millennia ago. Through a mixture of deception and scientific skill, the crew are able to neutralise Apollo’s powers and escape his grasp, forcing him to finally move on and join the rest of his people — though Kirk wonders if it would have hurt them to indulge him for just a little while.
8. The Horta
When the Enterprise is called to Janus VI to investigate the presence of a hostile alien, Kirk and Spock become engaged in a tense hunt through an expansive underground mine, stalked at all times by a silicone-based lifeform which secretes an acid that not only allows it to glide through solid rock, but also burn its victims to a crisp. Though the Horta seems terrifying at first, Kirk ultimately chooses to show the creature compassion, and learns that she is a highly intelligent alien who killed only as a desperate last resort to protect her eggs. After Kirk manages to hash out the beginnings of a treaty between the Horta and the miners, the Horta and her offspring become firm allies of the Federation.
7. Romulans
The Romulans would eventually become a staple of the franchise, appearing frequently in The Next Generation and Deep Space Nine. But in their first appearance in the episode “Balance of Terror,” the Romulans are an unseen and deadly opponent. The Enterprise becomes locked in an hours-long battle with a Romulan ship of equal strength, both captains striving to outwit and overcome the other, with the threat of galactic war hanging in the balance. The Romulan commander will stop at nothing to destroy the Enterprise, even launching an ancient nuclear warhead at the ship.
6. Gorn
Featured in the episode “Arena,” the first sign of the Gorn is the destruction they leave at the peaceful Federation colony of Cestus III — their attack leaving little behind but ruins and corpses. Enraged, Kirk gives chase to a fleeing Gorn ship, and the intervention of a powerful alien third party forces him into one-on-one combat with the Gorn captain. Once again, though, Kirk puts aside vengeance and allows peace to win the day, and the episode ends with the hope of better relations between the Gorn and the Federation in the future.
5. Trelane
The sole resident of the planet Gothos, Trelane is an all-powerful alien who styles himself as a 19th century British aristocrat with military pretensions. Though hospitable at first, Trelane quickly reveals that the Enterprise landing party are doomed to remain his guests and playthings until the day they die. The reasoning behind Trelane’s erratic behaviour becomes clear in the famous twist ending.
4. The Melkotians
The ultra-xenophobic Melkotians regard all outsiders as a “disease” which “must be destroyed” — a fact Kirk learns only too late after meeting one of them face-to-face. They sentence Kirk and his party to death, but rather than simply executing them, the Melkotians instead trap them in a terrifying illusory world, in which they are cast as the Clanton gang on the day of the gunfight at the O.K. Corral, and their deaths seem imminent and inescapable. Once again, an unexpected show of mercy from Kirk saves the day, and the Melkotians ultimately find themselves more agreeable to further talks with the Federation.
3. The Salt Vampire
The M113 Creature — typically known as the “Salt Vampire” by fans — is a shapeshifting alien that feeds on the salt inside the human body, leaving its victims as disfigured pale corpses. It’s probably best remembered for the scene in which its horrifying true appearance is at last shown, while it attacks Kirk. Despite everything, the creature was not entirely unsympathetic — it was said to be the last of its people, and its home-world was covered in the ruins of a once-great civilization. Some fans argue that it was simply trying to survive at any cost.
2. Dikironium Cloud Creature
On the planet of Tycho IV lurks a predatory, sentient cloud, which envelops its victims and drains them of all the red blood cells in their body. The stakes are personal for Kirk in the aptly-titled episode “Obsession” as he faces the cloud for the second time in his career. As a young officer, he witnessed the cloud decimate the crew of the USS Farragut, and is now unrelenting in his desire to destroy the creature at any cost.
1. The Doomsday Machine
The Doomsday Machine — or the “planet-killer” — is a piece of alien technology and a weapon of unimaginable destruction. Kirk theorises that it could be “a doomsday machine that somebody used in a war uncounted years ago. They don’t exist anymore, but the machine is still destroying.” It glides through space, consuming entire planets to fuel itself and continue its path of destruction. The Enterprise crew first learn of it when they discover their ruined sister ship, the USS Constellation. The only survivor is the ship’s captain, Matt Decker, who has lost his mind after his ship was disabled and his entire crew killed by the entity. The planet-killer proves invulnerable to any and all attacks, and is set to carve a path straight through one of the most heavily-populated areas of the galaxy, until the crew develop a risky solution.
