The 20 Best Episodes of ‘Star Trek: The Original Series’

8. “The Enemy Within”

“He’s like an animal. A thoughtless, brutal animal. And yet it’s me. Me!” – Kirk

Star Trek takes on Dr. Jekyll and Mister Hyde in a sci-fi context in an episode that delivers a classic performance by William Shatner. During a survey of the planet Alpha 177, a technician is exposed to a magnetic ore that alters the function of the Enterprise’s transporter. When Kirk beams aboard the ship, the transporter splits him into two beings: one good, one evil. After the new animalistic Kirk attempts to force himself on Yeoman Rand, Spock deduces that there is an imposter aboard the Enterprise.

Meanwhile, Kirk experiences problems with decision-making, while Sulu and three other crew members remain stranded on the planet’s surface. McCoy informs Kirk that all humans have a dark side to them and that his strength of command lies in his negative self. After a confrontation on the bridge where it’s unclear which Kirk is which, Evil Kirk eventually breaks down under the strain of the circumstances around him, crying out, “I want to live!” Kirk is materialized back into one person and the crew members below are beamed aboard the ship.

It’s difficult to take one’s eyes off William Shatner in this episode. Moving from hesitance to lustfulness, from violence to sorrow, Shatner delivers his most nuanced, albeit over-the-top performance in the history of Star Trek. The episode is also celebrated for its insightful look into the conflicting dualities of human nature. By the way, did I mention that a certain adorable alien canine gets divided into two adorable alien canines? This one is a must-watch.

7. “The Man Trap”

“Something wrong, captain?” – Spock

“I was thinking about the buffalo, Mister Spock.” – Kirk

The first episode of Star Trek to air on television, “The Man Trap” develops whimsical chemistry between our favorite crewmembers and features both a creepy monster-of-the-week and a gorgeous planetary backdrop. Kirk, McCoy, and a red shirt (Michael Zaslow) beam down to the planet M-113 to provide medical supplies to Dr. Robert Crater (Alfred Ryder) and his wife Nancy (Jeanne Bal), who just happens to be an old flame of McCoy’s. Mysteriously, each crew member perceives Nancy as a different woman from his past. Also odd is Dr. Crater’s intense desire for salt tablets. When the red shirt is found dead nearby due to a sudden lack of salt in his body, it becomes evident that McCoy’s former lover is not what she appears to be.

The wise-cracking between Kirk and McCoy about the past romance between Bones and Nancy immediately establishes Kirk as something more spontaneous than an authoritarian ship captain and Bones as a charmingly ornery country doctor. Spock’s logic-based personality is also fleshed out here, notably through a flirtatious scene between the Vulcan and Uhura, which may have inspired the romance between Uhura and Spock in the J.J. Abrams Trek films. Also showcased is Sulu’s interest in botany and Grace Lee Whitney’s beehive-touting Yeoman Janice Rand. The episode’s Salt Vampire is happily not simply a one-dimensional, clichéd monster, but rather an intelligent being, the last of its kind, following its natural survival instincts. The tragic existence of the Salt Vampire is sorrowfully compared to that of the buffalo.

6. “Balance of Terror”

“You and I are of a kind. In a different reality, I could have called you friend.” – Romulan commander

The U.S.S. Enterprise battles a Romulan ship suspected of destroying outposts in the Neutral Zone in a thrilling cat-and-mouse space opera based on the 1957 movie The Enemy Below, with the Enterprise taking on the role of the American destroyer and the Romulan Bird-of-Prey with its cloaking device playing the role of the submarine. Viewers learn that since two-way visual communications did not exist during the Earth-Romulan war of the recent past, Romulans and humans have never seen one another. Not only does the Enterprise have to confront a brilliant tactician, but it must also confront its own bigotry. When it’s revealed that the Romulan commander, brilliantly played by Marc Lenard (who later assumes the role of Spock’s father Sarek) resembles a Vulcan, Lieutenant Stiles (Paul Comi) begins to suspect that Spock is a Romulan spy.

Following the Romulan ship into a comet’s tail, the Enterprise and the Romulan ship exchange plasma torpedos and phaser fire. After Spock saves Stiles and the ship itself, severely damaging the Romulan vessel, Kirk and the Romulan commander share a moving scene in which the Romulan tells Kirk he admires him and that they could have been friends under different circumstances. Rather than accepting capture, the Romulan commander chooses to destroy his own craft and himself with it. One of the strongest episodes of Star Trek, “Balance of Terror” introduces a new alien race in the Romulans in a bold entry in the larger Trek mythos that showcases Kirk’s ability to outmaneuver his enemy under most dire conditions.

5. “Arena”

I shall be merciful and quick.” – The Gorn

Captain Kirk squares off against the Gorn captain in a battle of both might and wits on a desolate planet in one of the most enduring Star Trek episodes of all time. After the Cestus III Outpost is obliterated by a species of aliens, the Enterprise engages the aggressor ship. Suddenly, the Enterprise is contacted by a species of aliens called the Metrons (voiced by Vic Perrin) who zealously guard their sector of space against outsiders. They announce they will pit the respective captains of both ships against one another in a “trial by combat”, a one-on-one battle to the death, with the ship on the losing side to face destruction and the other ship free to leave. The captains are beamed down to a rocky desert planet with various resources that might be used to fight one another. On the Enterprise, the crew helplessly looks on while Kirk engages the reptilian Gorn (voiced by Ted Cassidy) in mortal combat.

In an episode centered on themes of survival and mercy, Kirk must learn to understand his enemy’s thought process and overcome the fact that he is wholly outmatched by a physically stronger opponent. While “Arena” is a thrilling and ethically interesting romp in space, it will forever be remembered for its amazing Gorn costume. Charming levels of ’60s science fiction cheese elevate “Arena” into the upper echelon of Star Trek lore.