Ever since William Shatner's Captain James T. Kirk first appeared in Captain of the USS Enterprise. Although Leonard Nimoy's Spock became arguably even more popular than his captain, neither character would be the same without the other. Captain Kirk remains a fixture of modern Star Trek, with Paul Wesley bringing new life to the character on Star Trek: Strange New Worlds.

Star Trek: The Original Series, however, undoubtedly made Captain Kirk who he is, and Kirk stars in many of the show's most iconic moments. Star Trek's TV series and movies.

15 "The Enemy Within"

Star Trek: The Original Series Season 1, Episode 5

William Shatner does double duty in "The Enemy Within," portraying two different versions of Captain Kirk. When a transporter malfunction splits Kirk into two distinct halves, one "good" and one "evil," the evil Kirk wreaks havoc on the Starship Enterprise. The evil Kirk masquerades as his counterpart, ordering the crew to abandon a landing party on the surface of the planet below.

Leonard Nimoy first proposed the Vulcan nerve pinch to knock evil Kirk out in this episode, as he did not think Spock would simply hit Kirk over the head.

The good Kirk eventually convinces his other half that they both need each other, and they are sent through the transporter and restored. William Shatner is over-the-top as the evil Kirk, but his performance remains iconic and it mostly works thanks to the premise of the episode. Evil Kirk's attempted assault of Yeoman Janice Rand (Grace Lee Whitney) and Spock's uncharacteristic "joke" regarding the assault are the only black marks on an otherwise solid episode.

14 "Amok Time"

Star Trek: The Original Series Season 2, Episode 1

In "Amok Time," Kirk grows concerned when Spock begins behaving strangely, eventually prompting the Vulcan to reveal that he is undergoing pon farr and must return to Vulcan. Despite orders to travel to Altair VI, Kirk changes course to Vulcan, placing his friend's life above his career. Kirk and Dr. McCoy travel to the surface to attend Spock's wedding, but Spock's fiancée T'Pring (Arlene Martel) demands the kal-if-fee ritual and chooses Kirk to fight Spock.

During the fight, McCoy secretly injects Kirk with a neuroparalyzer that makes him appear dead. Spock's joy upon realizing that he did not kill Kirk is one of the Vulcan's best moments, but Kirk gets some great moments, too. The fight between Kirk and Spock remains one of Star Trek's most memorable battles and the whole episode is a great exploration of the pair's iconic friendship.

13 "Court Martial"

Star Trek: The Original Series Season 1, Episode 20

The courtroom drama has become a staple of the Star Trek franchise, and "Court Martial" stands as one of the show's earliest examples. When Captain Kirk is court-martialed and accused of purposely ejecting a research pod containing Lt. Commander Benjamin Finney (Richard Webb), he faces a court-martial. Things look grim for Kirk when the Enterprise computer seems to contradict the captain's version of events, but Spock soon realizes the computer may have been tampered with.

In the end, it's revealed that Finney orchestrated the entire thing as a way to get back at Kirk for a slight from years before. As Kirk and Finney had been friends at Starfleet Academy, "Court Martial" offers a rare glimpse into Kirk's life before he took over command of the Enterprise. Throughout the episode, Kirk stands firm in the knowledge that he did nothing wrong and is ultimately vindicated even as he laments the loss of his friend's sanity.

12 "Space Seed"

Star Trek: The Original Series Season 1, Episode 22

In hindsight, "Space Speed" is most ed as the episode that introduces the genetically enhanced tyrant Khan Noonien Singh (Ricardo Montalbán). But the episode is a great vehicle for Captain Kirk as well. "Space Seed" begins when the Starship Enterprise finds Khan's ship adrift in space with all engers kept in suspended animation. Upon waking, Khan almost immediately returns to his tyrannical ways and attempts to take over the Enterprise.

With his intelligence and cunning, Khan remains one of Kirk's greatest adversaries.

Khan seduces Enterprise historian Lt. Marla McGivers (Madlyn Rhue), and although she initially helps him, she later frees Kirk, allowing him to take back his ship. With his intelligence and cunning, Khan remains one of Kirk's greatest adversaries. The two eventually engage in an intense fistfight in engineering, which Kirk only wins because he uses a makeshift club to knock Khan out. In the end, Kirk strands Khan and his people on the desolate Ceti Alpha V, a decision that will come to haunt the Enterprise captain years later.

11 "A Piece Of The Action"

Star Trek: The Original Series Season 2, Episode 17

In one of Star Trek's funniest episodes, Captain Kirk and his crew visit a planet whose society is based on an Earth book entitled Chicago Mobs of the Twenties. Kirk, Spock, and McCoy get caught up in a gang feud between Bela Okmyx (Anthony Caruso) and Jojo Krako (Victor Tayback). Both crime bosses demand "heaters" (phasers) from Kirk, and Kirk eventually uses the Enterprise's weapons to show the gangsters how powerful his people are.

Kirk and Spock both don period-appropriate clothing, speak in classic exaggerated gangster accents, and ultimately help the two gangs overcome their differences. Kirk and Spock's initial confusion about their situation quickly turns into genuine enjoyment as they embrace their inner gangsters. From Kirk's attempt at driving a car (and Spock's trepidation about his driving) to his invented card game Fizzbinn, Shatner's Kirk is truly at his funniest in "A Piece of the Action."

10 "The Doomsday Machine"

Star Trek: The Original Series Season 2, Episode 6

When the Enterprise faces off against a planet-killing doomsday machine, Captain Kirk must get creative to find a way to stop it. The Enterprise encounters the USS Constellation drifting in space, with the ship's commander, Commodore Matt Decker (William Windom), as the only surviving crew member. As the more senior officer, Decker is given command of the Enterprise, but his guilt and shock make him unfit to lead. As his final act, Decker steals a shuttlecraft and flies straight into the planet killer in a suicide run.

Although some Star Trek tie-in materials state that Matt Decker is the father of Star Trek: The Motion Picture's Will Decker (Stephen Collins), this has yet to be officially confirmed in canon.

Although Decker's actions don't destroy the machine, Krik gets the idea to blow up the much larger Constellation within the planet killer to destroy it. Kirk himself pilots the Constellation into the maw of the machine, and one of his best moments comes when he calmly requests to beam back to the Enterprise even as the Constellation is about to explode. It's an intense moment that illustrates Kirk's obvious faith in his crew, even if they sometimes cut things a little close.

9 "The Trouble with Tribbles"

Star Trek: The Original Series Season 2, Episode 15

In another hilarious episode of Star Trek, the USS Enterprise visits Deep Space Station K-7 to guard a shipment of grain. While there, the crew visit the station for shore leave, and some of the crew get into a brawl with a Klingon crew. Meanwhile, Lt. Nyota Uhura (Nichelle Nichols) brings an adorable Tribble aboard the Enterprise that quickly multiplies into hundreds of Tribbles.

Worried that the Tribbles could threaten the grain, Kirk rushes to check on it only to be buried in an avalanche of the little balls of fluff. This scene has since become one of Star Trek's most iconic moments, and William Shatner proves once again that he has a talent for comedy. It's Chief Engineer Montgomery Scott (James Doohan) who gets the last laugh, however, when he beams all of the Tribbles onto the Klingon ship.

8 "The Corbomite Maneuver"

Star Trek: The Original Series Season 1, Episode 10

When the Enterprise encounters a spherical ship from the First Federation, Commander Balok announces his intentions to destroy Captain Kirk's ship. Thinking on his feet, Kirk makes up a substance called Corbomite that will destroy Balok's ship if he destroys the Enterprise. Kirk's bluff pays off, although Balok then tows the Enterprise with a tractor beam. Kirk breaks the Enterprise free but still answers the distress call from Balok's now-damaged ship.

Kirk, Dr. McCoy, and navigator Lt. Dave Bailey (Anthony Call) beam over to Balok's ship to discover that the intimidating being they saw on the Enterprise viewscreen was only a puppet. The real Balok (Clint Howard), who looks like a human child, reveals the entire encounter was a test, speaking with the voice and intelligence of an adult. Kirk is at his most clever in "The Corbomite Maneuver" and the episode has everything that makes a great Star Trek episode.

7 "Errand of Mercy"

Star Trek: The Original Series Season 1, Episode 26

"Errand of Mercy" introduces the Klingons, as Captain Kirk goes toe-to-toe with Commander Kor (John Colicos), who proves to be a worthy adversary for the Enterprise captain. In "Errand of Mercy," the Enterprise travels to Organia, a planet that lies on the border between the Klingon Empire and the United Federation of Planets. Kirk tries to convince the Organians that it would be better for them to ally with the Federation, but they refuse to get involved.

Kor made several return appearances in Star Trek: Deep Space Nine.

When Kor and the Klingons arrive, the Oraganians bow to their rule without complaint, despite Kirk's attempts to get them to rise up. The Organians eventually reveal themselves to be incredibly powerful incorporeal beings, and they force Kirk and Kor to end the conflict between the Federation and the Klingons. Kirk (and Shatner) always rise to the occasion when faced with a strong opponent played by a talented actor, and that is on full display here in all of Kirk's exchanges with Kor.

6 Star Trek IV: The Voyage Home

Directed by Leonard Nimoy, Star Trek IV premiered on November 26, 1986.

Star Trek's fourth feature film is also its most fun, as Kirk and his Enterprise crew travel back in time to save the world by saving some whales. With a dangerous probe affecting Earth's power grid, the song of the extinct humpback whale is the only thing that can stop it. Kirk and his crew devise a plan to travel back in time in their captured Klingon Bird of Prey using a slingshot maneuver around the sun.

As Kirk and his crew hilariously try to navigate 1986 San Francisco, they encounter Dr. Gillian Taylor (Catherine Hicks), who tells them of a pair of humpback whales that will soon be released back into the wild. All of the main Enterprise crew get fun moments throughout Star Trek IV: The Voyage Home, but Kirk and Spock's interactions with the locals are the most memorable. Kirk is clearly having fun throughout the film, and he's rarely been more charming.