The 1960s-1970s are considered the golden age for science fiction media. The first episode of Doctor Who premiered in 1963, and the first Star Wars movie hit theaters in 1977. Alongside these iconic triumphs was Star Trek, created and produced by Gene Roddenberry. The first iteration of the show, called The Original Series (TOS), introduced the Starship Enterprise, commanded by Captain James T. Kirk. The crew explores the galaxy and ensure peace between planets.

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The show was a massive success. It spawned multiple continuations, not only from Roddenberry, but from fan-made series and anthologies. In recent years, we've seen the newest installment, Star Trek Discovery, and Star Trek Picard, which revisits the captain from Star Trek: Next Generation. Over 50 years since its debut, Star Trek is still a sci-fi powerhouse. Let's take a look at some of the most unforgettable episodes from the series that started it all.

8 Amok Time

The second season opener revolves around Spock, the logical science officer and first officer of the Enterprise. He is half-human and half-Vulcan (as indicated by his pointed ears). He experiences a condition called pon farr, in which he must mate or die. Therefore he must return to his home planet, Vulcan, to participate in a wedding ritual. His fiancee, T'Pring, selects Kirk to fight Spock to the death for her hand in marriage.

Before we didn't know much about his Vulcan heritage, but this episode gives insight to Spock's character and background. This is also the only episode of the original series to show the planet Vulcan.

7 Space Seed

One of the most iconic scenes in all of The Original Series occurs in the second movie. Captain Kirk trembles with rage and yells: "KHAANNN!" All trekkies know the infamous Khan Noonien Singh, a dangerous and intelligent superhuman. But without "Space Seed", we would have never met him.

This episode from the first season introduces Khan, as he tries to take over the Enterprise. Kirk sends him into exile, which allows him to return in Star Trek II: The Wrath of Khan. He serves as a great foil to Kirk, who is also human, but wants to use his command for peace, not destruction. Not only have critics deemed it one of the best episodes in the series, but other Star Trek spinoffs reference this episode.

6 Plato's Stepchildren

Much like "Who Mourns For Adonis?" the setting of this episode takes inspiration from Ancient Greece. The plot concerns a race of telekinetic beings who call themselves Platonians in honor of the Greek philosopher Plato. Kirk, Spock, and McCoy arrive in peace, but the Platonians use their powers for evil. They control the members of the starfleet for their own amusement, specifically forcing Kirk and Lieutenant Uhura to kiss.

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This episode made history as the first scripted interracial kiss on television. Nichelle Nichols (Uhura) looks back fondly, saying it received an overwhelmingly positive response from fans. It was daring for the 1960s, but it is now among the most iconic and passionate kisses in television history.

5 Arena

If we wanted to introduce Star Trek to a newbie, we would show them "Arena". The Enterprise loses propulsion, and are contacted by aliens called the Metrons. Another ship is also arriving, and the Metrons pit the two captains of the ships against each other in a "trial by combat." A species called the Gorn inhabit the other ship, and now the Gorn captain and Kirk must battle.

For the sixties, the prosthetic work on the Gorn is pretty good, and genuinely looks intimidating. The Gorn is one of the most memorable foes in the show, up there alongside the Klingons and Romulans. The twist ending is when Kirk finds a way to kill the Gorn, but instead, he shows mercy. This encapsulates the entire purpose of the starfleet -- to demonstrate diplomacy with other planets and alien races -- and an even larger moral about forgiveness. This first season episode has it all: suspense, an alien battle, and a humane ending.

4 Trouble With Tribbles

How can anyone forget the tribbles? Most intergalactic foes were powerful and fearsome, but the tribbles proved antagonists can be cute and cuddly. In this episode, Uhura brings a tribble onto the ship, and everyone is enamored with them. The trouble begins when they start multiplying at a rapid rate, and then start dying due to a virus in their grain. Yet the tribbles help Kirk identify a Klingon spy aboard the Enterprise, and the crew delivers them to the Klingon vessel.

This episode is memorable for its lighthearted and comedic approach, and of course it's adorable, furry fiends. It is often ranked among the top five or ten "must see" episodes of the series.

3 Mirror Mirror

What if the members of the Enterprise aligned with evil? This episode considers an alternate universe where this is true. A transporter malfunction swaps Captain Kirk with his evil counterpart in another universe. The acting in this episode is superb, especially from Nichelle Nichols, Leonard Nimoy (Spock), and Walter Koenig (Chekov).

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The"mirror universe" concept became a hallmark for future episodes of the show, especially in the new Discovery reboot. It became a staple in the realm of science fiction, as well as in literature and comic books. It offers a concept we would have never considered, and we're kept on our toes as we watch our Kirk interact with the evil crew, and our crew interact with the evil Kirk. We also have to admit the alternate costumes in this episode are great. And admittedly -- Spock with a beard is pretty sexy.

2 The Enemy Within

While this episode is similar to "Mirror Mirror," it centers around Captain Kirk. A transporter malfunction (another one?) causes Kirk to split into two different people. One is good, but he is weak and futile, and the other is "bad," but he is strong and effective. The evil half causes mayhem on the ship, while the good half tries to stop him. Even though the crew helps the good one overpower the bad one, Kirk states they will both live on as parts of each other.

This is a great moment for Kirk, and a powerful consideration in general: there is good and evil in all of us. Not only does this episode give insight into Kirk's character, but William Shatner does an incredible job portraying both iterations. It's an episode that makes you think, and is must see if you love Kirk.

1 City on the Edge Of Forever

We saved the best for last. A crazed McCoy escapes to an abandoned planet, where the crew discovers a time portal replaying Earth's history. Bones jumps through it, causing the Enterprise to disappear as a result of altering time. Kirk and Spock go through and end up in the United States during the Great Depression. They must stop McCoy from interfering with this crucial time in history.

This episode introduced how time travel might cause consequences for the future, also depicted in Doctor Who and Back to the Future. It involves a touching romance between Kirk and Edith Keeler, a woman from the Depression, as well. This episode won several awards, and Roddenberry claimed it one of his favorite episodes to work on. It is considered to be the best episode of the original series, period.

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