"'All I ask is a tall ship, and a star to steer her by.' You could feel the wind at your back in those days, the sound of the sea beneath you. And even if you take away the wind and the water, it's still the same... The ship is yours, you can feel her. And the stars are still there, Bones."
Kirk, "The Ultimate Computer"
The Captain. James Tiberius Kirk leads his ship, the Enterprise, through the adventure of the week—hostile cultures, supercomputers, places which look suspiciously like Earth, time-travel shenanigans. He was notorious for his many brief romances, some of which ended tragically, but mostly they failed because he named the Enterprise herself as the woman in his life. Although he took the dangers to his crew very seriously, he also maintained a light-hearted attitude and bantered with the other two members of his Power Trio frequently.Although boldly going and playing by his own rules worked out pretty well during the height of his career, the movies Deconstructed his legend by showing how high the cost of such cavalier actions could be.
Anti-Hero: Sixties sex symbol or not, Kirk stumbled into Classical Anti-Hero in The Wrath of Khan where his mid life crisis wears heavy and some poor choices cost the lives of many recruits (and a bulging waistline and receding hairline didn't do him any favors...) and Knight in Sour Armor in The Undiscovered Country and Star Trek 2009.
Badass Normal: Kirk is a good tactician who leagues of more powerful aliens respect, whose exploits include beating a bio-engineered superman with his bare fists. Did we mention he's a non-powered human?
A Running Gag in the movies is Kirk's loving relationship with his chair. He glumly sits in the rickety Captain's chair aboard the Enterprise-A, declaring that it's just not the same. Generations repeated this gag onboard the Enterprise-B, this time complete with Male Gaze.
Legendary in the Sequel: Kirk is depicted as the Captain, against which all of his 24th-century successors are judged.
Living Legend: Even though the original series depicts his first command, it's clear that he's already becoming one of these. The movies take this trope and run with it.
Married to the Job: His commitment to the Enterprise is so overpowering he doesn't even need an antidote to a love potion.
Mr. Fanservice: That uniform shirt of his will tear open at the touch of a twig. This was not actually intentional; its just that the tailoring budget for the original show was less than impressive.
The Not-Love Interest: Spock seems comfortable being physically close to Kirk or locking gazes with him. Edith Keeler said that Spock belonged "at his side, as if you've always been there and always will." But his established romances have always been with females, and at one point he invited Kirk to his wedding.
Shirtless Scene: It's not quite to the level of Walking Shirtless Scene, but Kirk appears shirtless a lot in the original TV show. Mostly famously, it's caused by Clothing Damage during action sequences, but he also tends to just lounge around his quarters without a shirt and such.
Sudden Name Change: In the second pilot episode crewman Mitchell, possessed of near-omnipotent alien powers, fights Kirk and creates an open grave with a tombstone reading "James R. Kirk". This would normally be a minor matter but given how many times Kirk later introduces himself as "James T. Kirk" it's actually quite jarring.
Ultimate Job Security: Later crews even lampshade that Kirk shouldn't have been able to get away with so much.
Verbal Tic: His peculiar speaking style is perhaps the most famous (and certainly the most frequently-parodied) thing about him. A combination of Gratuitous Iambic Pentameter and Punctuated! For! Emphasis!, along with inappropriately-placed pauses, which are almost always followed by delivering the rest of his line in rapid-fire fashion.
Commander Spock (Leonard Nimoy)
"Fascinating is a word I use for the unexpected. In this case, I should think 'interesting' would suffice."
Spock, "The Squire of Gothos"
Kirk's Number One and science officer. Spock was half-Human, half-Vulcan, and chose to completely embrace the latter aspect of his heritage. This caused him to clash frequently with Dr. McCoy. Spock was supremely analytical and would describe many things as "fascinating;" he was the go-to man for unusual solutions... or ruthlessly pragmatic ones. He would, occasionally, let slip his more human feelings, but regarded any comparison with humanity to be insulting during the show's run.Despite the stark contrast in their personalities, Spock and Jim were very good friends (so much so that they inspired Slash Fic in 60's and 70's fanzines). The character became so iconic that Nimoy put out an autobiography titled "I Am Not Spock," although he later embraced the fanbase. He has reprised the character in Star Trek: The Next Generation and the 2009 Star Trek movie.
Ambiguously Jewish: Many fans think that Spock is Jewish on his human mother's side as Leonard Nimoy is Jewish, not to mention that Winona Ryder (who played Spock's mom Amanda Grayson in the 2009 reboot) is Jewish as well. On a related note, Nimoy adapted the famous Vulcan hand salute from Jewish religious tradition.
Arranged Marriage: Betrothed by his family as a child. His intended bride has other ideas, and doesn't mind sacrificing Kirk for them...
Bizarre Alien Biology: Principally his green blood and the fact that his heart is where a human's liver would be. The latter enables him to survive being shot in the back with a flintlock rifle in "A Private Little War".
Blue-Green Blood: Not explicitly stated, but his father is a prestigious Federation Ambassador, and T'Pau, one of the most powerful people on Vulcan, officiates at (what should have been) his marriage. He also notes that the large estate where the ceremony takes place has been in his family for over two thousand years.
Boomerang Bigot: Is half-human, but most of the time solely embraces his Vulcan heritage and is scornful of human ways. This was later explained in backstory due to his rocky relationship with his father and the Fantastic Racism he experienced whilst growing up on Vulcan. He mellowed in his later years.
But Not Too Alien: He's half-human; while he usually acts fully Vulcan, his human side surfaces fairly often.
Captain Ersatz: Spock's personality is an exaggeration of Roddenberry's former boss, LAPD Chief William H. Parker.
The Creon: Spock is this, almost to the letter. He only takes command of the Enterprise once Kirk has been Kicked Upstairs, and gives it back almost immediately when the opportunity arises. And, being already a captain and in command of the Enterprise, Spock never gets his own commission: he keeps his position as first-officer under Kirk for several more movies! Surprisingly, Spock's mirror-universe counterpart is exactly the same on this - and even explicitly states his reasons (in "Mirror Mirror"). note Namely that he preferred being "a lesser target" for Klingon Promotions.
Subordinate Excuse: Spock's friendship with Kirk may be an explanation for why Spock continues to serve as Kirk's first officer even after he is promoted to Captain himself.
Deadpan Snarker: Apparently there is nothing illogical about scathing sarcasm. Despite his claims to be above human pettiness, Spock frequently makes sarcastic quips or the "really?" face.
Deuteragonist: A natural result of his popularity with fans; originally, the show was intended as having plots about "Kirk and X", where "X" would be a different character each week; many of the early first season episodes follow this formula, but gradually "X" and "Spock" became interchangeable.
Escapist Character: To socially awkward Trekkies. Spock is smart, respected, physically powerful, long-lived, and blessed with loving and devoted friends even though he himself has never learned human social skills.
Forgets to Eat: Occasionally. While never shown, in "Amok Time", McCoy uses the fact that Spock hasn't eaten for three days in an attempt to convince Kirk that something is wrong, and Kirk dismisses it as simply being Spock in one of his contemplative phases. Another example is "The Paradise Syndrome", where Spock hardly eats for weeks while studying the obelisk.
McCoy: Spock, you are the most cold-blooded man I've ever known.
Spock: Why, thank you, Doctor.
Living Legend: Invoked in "Amok Time" when T'Pring informs Spock that he has become a legend among the Vulcans, and that she has no desire to become the consort of a legend. His status only grows through his efforts to achieve a lasting peace with the Klingons, and his subsequent ambassadorial career. In the later shows, he is depicted as Legendary in the Sequeleven though he is technically still alive throughout the franchise (including into the reboot continuity).
Ludicrous Precision: Will often give time estimates down to the second and can complete large exponential multiplications in his head.
He gets a moment in Star Trek VI: The Undiscovered Country when Valeris, his protege, is revealed to be the conspiracy's mole on board the Enterprise. She has a phaser drawn on him, and when she refuses to shoot, he slaps it out of her hand with a clear look of anger on his face.
Super Strength: The Vulcan heritage makes Spock three times stronger than a human.
Token Nonhuman: He's the only regular in the cast who is visibly nonhuman. (The animated series averted this since there was no make-up budget in the way.)
Verbal Tic: His endless permutations of the word "logic", and his unfailing ability to fit them into sentences, border on this.
Vitriolic Best Buds: With McCoy. That Spock considers him a close friend is established beyond all doubt in "Amok Time", when he invites him (along with Kirk) down to Vulcan to witness a ceremony which is deeply private and personal to Vulcans.
The Worf Effect: Any enemy that can hold Spock in a fight is deemed a formidable adversary.
Doctor (Lieutenant Commander) Leonard "Bones" McCoy (De Forest Kelley)
""I signed aboard this ship to practice medicine, not to have my atoms scattered back and forth across space by this gadget."
McCoy, "Space Seed"
The third member of the Power Trio. Nicknamed "Bones" by Kirk, McCoy was a highly competent doctor who wasn't entirely comfortable with deep space and always brought a more emotional and moral component to the philosophical debates. He clashed frequently, and colorfully, with Spock, as he found Spock's rejection of emotion to be absurd. However, the two men did genuinely respect each other. Despite his "down-home country doctor" routine, McCoy could and did carry moments of Badassery frequently.Despite a very wild appearance in the first one, McCoy remained largely the same in the movies: a cantankerous but kind-hearted medical professional.
Badass Pacifist: He's a doctor and takes that very seriously. However, that doesn't stop him from doing extremely dangerous things to save lives. Circumstances sometimes force him to show that he is a decent shot and somewhat competent brawler, but he is hardly a willing Combat Medic, both disgust with violence and unashamed fear always extremely apparent on his face. Possibly best seen in "Space Seed," where he doesn't flinch at Khan holding a knife to his throat and even gives advice on the best way to kill him from their current position.
Frontier Doctor: Dr. McCoy is perhaps Trek's outstanding example of a (Final)Frontier Doctor—resourceful in the face of alien ailments, preferring simple homespun methods when possible, but cantankerous, eccentric, and not entirely happy with his lot (he fled to space on the heels of a divorce). Star Trek was pretty much the originalSpace Western, after all, and actor DeForest Kelley had an extensive background in westerns.
Good Is Not Nice: He's not hesitant about expressing his dislike for people or his refusal to suffer fools but he is most often the one who suggests doing the right thing.
Good Old Ways: He both enforces and subverts this trope. He's rabidly in favor of fighting the dehumanizing effects of too much technology (especially the transporter) in favor of enjoying "the simple things in life", and yet sees "primitive 20th-century medicine" as just above trepanation, leeches, and blood-letting in its barbarity, preferring the "high tech approach" to healing. In general, he embraces the positive, constructive aspects of technological progress rather than the destructive or dehumanizing ones.
Grumpy Bear: McCoy is constantly grumbling about space travel, supercomputers, Spock, unruly patients, etc etc.
Hypocritical Heartwarming: McCoy is always trying to get an emotional rise out of Spock, but in the episode "Plato's Stepchildren," McCoy jumps to Spock's defense when powerful aliens force him to cry and to laugh. And in other episodes he's usually the first to jump to Spock's defense any time anyone attacks or insults him, possibly because his issues with Spock are more of a giant angry moral debate while other people tend to be full racism.
Innocent Blue Eyes: Doctor McCoy has DeForest Kelley's bright, shining baby blues. He's probably the kindest, most compassionate character of the entire Trek franchise.
In-Series Nickname: "Bones" is actually short for "saw-bones", an archaic term for a surgeon. It was originally intended as the nickname of Dr. Boyce from "The Cage", but was never used in that episode, making it available for McCoy.
More Hero Than Thou: In "The Empath" when aliens offer Kirk the choice of sacrificing McCoy or Spock, McCoy takes out Kirk with drugs. Spock is glad; since this leaves him in command, he can make the sacrifice himself. McCoy proceeds to drug him as well and sacrifice himself.
The Watson: Despite serving on Starfleet's flagship, McCoy is routinely unfamiliar with various technical aspects of the ship or other technology he encounters. (He is an excellent doctor, however, which makes up for it.)
What Could Have Been: An episode exploring his Backstory was planned and shelved at least twice. One of the main points (that he joined Starfleet as an established MD after a nasty divorce) finally saw the light of day in the 2009 movie.
McCoy was also supposed to have an estranged daughter named Joanna, who would have appeared in - and who's name was the original title of - "The Way to Eden", being one of the hippies who take over the Enterprise. Ultimately, she never appeared in the series, only showing up (possibly non-canonically) in The Animated Series.
Lieutenant Commander Montgomery "Scotty" Scott (James Doohan)
"I cannae change the laws of physics! I've got to have thirty minutes!"
Scotty, "The Naked Time"
Chief Engineer of the Enterprise. Scotty's most frequent job was to solve a seemingly-impossible crisis with the engine or transporters (or whatever piece of Starfleet technology was making trouble that week), protesting all the way before either hitting on a creative solution or sweating it through. He was also Scottish and had many sterotypical Scottish traits, such as a love of good whiskey and namedropping haggis. Though he was sometimes used for comic relief, it's worth noting that Scotty was extremelyBadass whenever he was the ranking officer on the Bridge and kept it safe from interfering aliens or Starfleet's many half-crazed admirals.Scotty's role in the films was still the Chief Engineer, but he was relegated to the comic relief role more often. He also appeared in an episode of The Next Generation.
Actor-Shared Background: James Doohan had a degree in Engineering and even used it to save Gene Rodenberry from danger when they went out boating and ran into trouble. No record exists of him saying that the boat "cannae take much more of this" though.
Badass: Any time he gets put in charge of the Bridge.
Beam Me Up, Scotty!: Scotty is universally remembered as complaining that the engines "cannae take much more ah this, Cap'n", for fear that "she's gonna blow", or some variation thereof. He's also known to protest that "ah doon have th' pow'r, Cap'n!" He never used any of those phrases on the show; they're cobbled together out of a dozen different lines from different episodes, and have become ubiquitous in parodies ever since.
He also said "Ah cannae change the laws of physics", and not "Ye cannae". That's from Star Trekkin'.
He didn't say either. He said, exactly, "I can't change the laws of physics. I've got to have thirty minutes!" Most parodies play the accent up far beyond the original.
Butt Monkey: Sometimes, whenever he was left in charge of the Enterprise.
Companion Cube: If Kirk saw the Enterprise as a demanding wife, Scotty saw the ship — particularly her engines — as no less than a child ("My bairns! My poor bairns!").
Dangerously Genre Savvy: Whenever he was left in command of the Enterprise. There's "Fool me once, shame on you, fool me twice, shame on me," and of course the time that he receives a word message from "Kirk" and the first thing he does is run it through a voice analyzer which proves it wasn't really Kirk. Do not fuck with Scotty.
The novel Kobayashi Maru reveals that Scotty's solution to the Kobayashi Maru was to reprogram the simulation to allow him to use a strategy that would never work in reality, which his instructors would immediately realise. After taking note of his ingenuity, they'd proceed to "punish" him by switching him from the command track to engineering... just as Scotty intended.
A Day in the Limelight: "Wolf In The Fold", "The Trouble With Tribbles", "By Any Other Name," and "The Lights of Zetar."
Uhura: Mr. Spock, I haven't done anything like this in years. If it isn't done just right, I could blow the entire communications system. It's very delicate work, sir.
Spock: I can think of no one better equipped to handle it, Miss Uhura. Please, proceed.
Uhura and Spock, "Who Mourns for Adonais?"
Uhura was Enterprise's communications officer and according to Gene Rodenberry was fourth in line of command behind Mr. Scott (not that this ever got displayed on the series). Unfortunately, her character was vastly underutilized during the series' run, although the times she was allowed to do more than be the ship's phone operator, she was pretty good at whatever she was doing. Her role was somewhat expanded after the first season and she did get to take the Captain's chair in the animated series.Offscreen, Nichols was subjected to racist harassment and resigned when she learned that the studio executives had been withholding her fan mail. A conversation with Martin Luther King Jr. convinced her to stay: he told her that the idea of a black woman being equal to whites was something vitally important for children to see, as a role model or as an example of what should be. Both Mae Jemison (America's first black female astronaut) and Whoopi Goldberg have cited her as an influence, along with many others.
Action Girl: In "Mirror, Mirror" and "The Gamesters of Triskelion."
Bridge Bunny: To Nichols' frustration. She did have a few episodes where she was on the away team but for the vast majority of the show, she was confined to her station.
Canon Immigrant: Her first name "Nyota" was used in the non-canon novels for decades before finally being made official. Very early Trek guides suggest that "Penda" was considered a possibility by the fans. Parodied in the 2009 film when Uhura refuses to tell Kirk her first name until the end of the movie.
The helmsman, thankfully living in a time before bridge consoles were Made of Explodium. Sulu was an affable and level-headed officer, a staple of bridge drama and away missions. He worked well with other members of a crew and sometimes shared his hobbies: botany, antiquing, and fencing. (Although the last one was not exactly in a clear state of mind.) When Chekhov was added to the crew, they formed a Those Two Guys dynamic.Although he has a Japanese first name, his surname is deliberately ambiguous; it is the name of a sea that borders several Asian countries. Like Uhura, Sulu was significant for being a non-stereotypical portrayal of an Asian man.
Canon Immigrant: His now-canon first name "Hikaru" was given to him in the non-canon novels by Vonda McIntyre. Very early Star Trek guides suggest that "Walter" was considered as a possible first name during the show itself, but never officially used.
Fake Nationality: Averted, for the only time in all series. Sulu is Japanese-American from San Francisco, and so is George Takei. Played straight in the 2009 film.note They were leery of casting an actor of non-Japanese descent until Takei himself assured them that it would be all right, claiming that the character represents all of Asia (note that Sulu is not a Japanese name). This paved the way for Korean-American John Cho to assume the role.
In some of the non-canon novels, Sulu explains that his background is mixed, but primarily Filipino and Japanese.
Katanas Are Just Better: Averted in "The Naked Time". Sulu was originally supposed to go on his rampage with a samurai sword, but at Takei's request to do something less stereotypical, it was switched to an epee.
Sadly played straight in the reboot movie - it's not exactly a normal katana, but it seems clearly intended to invoke this trope.
The Reliable One: He's quite competent at a variety of tasks, and very level-headed compared to characters like Chekhov or Scotty. He's also fiercely loyal to his crewmates, to the point of disobeying Starfleet orders and potentially causing a serious diplomatic incident just to rescue them.
Why Do You Keep Changing Jobs?: Initially the show's creators couldn't make up their mind what to do with Sulu, and he featured prominently as the ship's physicist in the second pilot before becoming the helmsman.
Word of Gay: Inverted. After Takei came out of the closet, many people assumed Sulu was also gay. Takei has denied that in interviews, claiming Sulu was/is straight.
As an interesting coincidence, Sulu is the only one of the six male regulars who never had an on-screen love interest, so there's no "proof" either way (Mirror Sulu, on the other hand, is obviously attracted to women, as Uhura can attest). The nearest he gets is some light flirting with Yeoman Rand during "The Man Trap".
Non-canon sources variously give Sulu a wife or make Demora the product of a Kirkesque fling.
Takei has also stated that Gene Roddenberry "knew that I was gay, and it never made a difference to him." This in The Sixties.
Ensign Pavel Chekov (Walter Koenig)
"Of course, Doctor. The Garden of Eden was just outside Moscow. A very nice place. Must've made Adam and Eve very sad to leave."
Chekov, "The Apple"
The ship's navigator from season 2 onwards. Chekov had a tendency to refer to Glorious Mother Russia and claim that any human advancement, technological or cultural, originated there. He also had terrible luck and frequently ran foul of whatever physical or psychological menace the ship was facing that week, mainly because Walter Koenig had an excellent capacity for screaming. Aside from that, he and Sulu were good friends and would frequently banter about the action.Chekov is by far the most junior of the regular bridge officers, but the writers justified his presence by having him act as the relief science officer whenever Spock was busy or incapacitated. In fact, Chekov would often abandon his navigation console in order to take up the science scanner if Spock had to step away - even at warp, or in the middle of a battle. In Star Trek III, in a nod to this, Chekov identifies himself as the "Acting Science Officer" of the Enterprise.Chekov was added for a few reasons: to attract younger viewers and give a nod to the Russians in the space race. (Also to fill in some of Sulu's role while Takei was filming The Green Berets).
Butt Monkey: Chekov did more screaming-in-pain than the rest of the crew combined. He even got a torture scene in the episode "Mirror, Mirror". This was explained as a convenient way to show there was mortal peril. Apparently, Kirk, Spock and McCoy all being older, dignified men would have made it improper for them to scream, but Chekov is in his early twenties and still very boyish, so it's all right for him. Doesn't make it any easier on the poor guy, though. In a nice inversion, he's the only one who doesn't get hit with the aging disease in "The Deadly Years". He still ends up getting subjected to a thousand and one medical checks, though.
Chekov: Blood sample, Chekov! Marrow sample, Chekov! Skin sample, Chekov! If ľ if I live long enough, I'm going to run out of samples!
Sulu: You'll live.
Chekov: Oh yes, I'll live. But I won't enjoy it!
Chekov's Gun: Often seen with Chekov, especially on landing-party duty. Like Chekhov's Gun, if it makes an appearance, it will most likely be used by the end of the episode or movie.
Cloudcuckoolander: Chekov's constant references to Mother Russia appear to only make sense in his mind.
The Scream: Walter Koenig had a good one, which is why it's Chekov who always gets stuffed into the agony booth, shot, driven insane, tortured by Klingons, implanted with parasitic worms...
Koenig lampshaded this by jokingly calling the second movie in the series "Star Trek II: Chekov Screams Again"
Sixth Ranger: Subverted. Chekov didn't appear on the show until Season 2, but apparently served on the Enterprise long before he appeared, because in the second movie, Khan recognizes Chekov, apparently having met him in the Season 1 episode "Space Seed".
Walter Koenig's explanation for how they met is that Chekov actually was serving aboard the Enterprise but was on duty during the night shift, and he and Khan met off-screen. The circumstances of their meeting were thus: Chekov was using the bathroom and he was taking an inordinately long time, and Khan approaches that very same bathroom, needing to use it. Finding it occupied, he soon loses his patience and pounds on the door. When Chekov finally emerges, Khan grabs him and fixes him with a Death Glare, and says "I will never forget your face!"
This is further compounded by the fact that he expended all the toilet paper.
No Rank Given: In the series, Chapel was always addressed by her position rather than her rank. She is formally promoted to Lieutenant later on in the five-year mission, and by the time of the first movie, has an MD under her belt, and is prepared to assume the role of Chief Medical Officer. We can therefore assume that, especially given her position as Head Nurse, she was a junior officer (probably a mustanged Ensign, given her backstory).
Real Life Writes the Plot: Majel Barrett was the girlfriend and eventual wife of Gene Roddenberry, which may explain why we saw Nurse Chapel so much. In part her role was also expanded in the latter half of the first season (after only sporadically appearing in the early episodes) due to Grace Lee Whitney leaving, and Nichelle Nichols also threatening to quit, which would have left the show without any recurring female characters.
Single Woman Seeks Good Man: Roger Kirby, her fiance, was a man two whom "life was sacred" by her own description. Given that her reasons for crushing on Spock included his honesty, it seems this applies across the board for Chapel.
The Bus Came Back: She became the Transporter Chief in the first film, had a cameo in Star Trek 3, and was Captain Sulu's communications officer in Star Trek 6. She also appears in a flashback episode of Voyager set during her time serving on board Sulu's ship.
Hypercompetent Sidekick: Implied—there are several references to her ability to keep Kirk from being swamped in paperwork, and one to improvising with a phaser when the food systems won't provide hot coffee.
Ms. Fanservice: The original media package described her as having "a strip queen's figure that a uniform can't hide." Not that those uniforms hide much, but whatever.
Satellite Character: With the exception of "The Man Trap", where she hangs around with Sulu for a large part of the episode, and "Charlie X", where she's the unwanted focus of Charlie's attraction until he (temporarily) zaps her out of existence, she has no significant interaction with any character other than Kirk.
Mauve Shirt: Because he was the only recurring redshirt not played by an extra, he usually had much more dialogue than other redshirts, a consistent name and position on the ship, and was allowed to play an active role in the plot (see "The Doomsday Machine" or "Mirror, Mirror" for examples).
Teleporters and Transporters: Contrary to popular belief, he was the Transporter Chief, not Scotty. Like other redshirts, he was occasionally seen on the bridge, though usually he was explicitly pinch-hitting for someone else (as in "Who Mourns For Adonais?" when Spock has taken command and Chekov is in the landing party, and Kyle mans the science station).
What Happened to the Mouse?: We never see him on-screen again after being marooned on Ceti Alpha V, which caused much speculation about his fate. The non-canon novels and comics established that he survived his unwanted shore leave on the planet, and eventually ended up on the Enterprise-A.
Kevin Thomas Riley (Bruce Hyde)
Ascended Extra: Actor Bruce Hyde was cast as a crewman with a significant part in "The Conscience of the King" without anyone realizing he had also played uber-Irishman Riley in "The Naked Time". When the producers finally realized this, the script was hastily re-written so that Hyde played the same character in both episodes. (The same thing happened with actress Barbara Baldavin, who appeared three times as Angela Martine but is accidentally addressed by other names more than once due to rewrites; figuring out who she really is almost approaches Continuity Snarl levels.)
Oireland: Got his "Irish" up when under the influence of the mind virus in "The Naked Time."
Real Life Writes the Plot: The reason Riley never returned after "The Conscience of the King", despite being very popular with fans, was that the actor left to become a hippie. Yes, really. Remember, this was 1967.
Ambassador Sarek (Mark Lenard)
Father of Spock. A distinguished Vulcan Diplomat, he and Spock were not on speaking terms for some time prior to the former's first appearance in "Journey to Babel" (to the point where Spock never even mentioned to Kirk or Bones that they were related). Sarek had wanted his son to follow him in his footsteps by attending the Vulcan Science Academy, but instead, Spock chose to join Starfleet.
Ambadassador: He's proficient in Vulcan martial arts. Spock points out that he could be a plausible suspect in the Tellarite ambassador's murder since Sarek knows the technique that killed him.
Blue Blood: Or at least comes from good family, in so far as Vulcans count such things, and behaves in a courtly manner.
Happily Married: Though Sarek and his human wife, Amanda, have their differences (as seen in "Journey to Babel"), and though he's culturally inhibited from expressing his emotions, it's clear the couple love each other very much.
Hey, It's That Guy!: In addition to Sarek, Lenard also played the Romulan commander in "Balance of Terror" and a Klingon captain in the first movie. He is the only actor to portray representatives of all three major galactic powers in the TOS continuity.
Not So Stoic: With a side order of OOC Is Serious Business. In Star Trek III, he's visibly angry when he confronts Kirk about the latter's supposed failure to return Spock's katra to Vulcan. This only escalates when he figures out Kirk has no idea what the hell he's talking about.
Affably Evil: He's a shameless crook and totally unrepentant scam artist, but he's friendly, cheerful, easy-going and surprisingly likeable, so long as you remember never to trust him with anything — especially anything worth money.
Con Man: His first appearance is based on his scam to marry gorgeous women secretly modified with drugs to be super-beautiful to lonely, wealthy space-workers for a huge payout. In Star Trek: The Animated Series, it's mentioned he once tricked an alien species by selling them the Starfleet Academy building.
Honest John's Dealership: The first storyline involving him is his plan to sell brides to lonely space-miners ( after giving them illegal "Venus Drugs" to make them super-beautiful). He'd also been convicted as a smuggler prior to his first appearance.
Loveable Rogue: He's a money-grubber and irresponsible, but he's affable and rarely trying to commit "truly evil" crimes.
Recurrer: He holds the distinction of being the only non-Starfleet character in the entire series to appear in more than one episode.
Trickster: He tries to be one, but he... doesn't really succeed at it. At least, not when he crosses Kirk's path.
Khan Noonien Singh (Ricardo Montalban)
"Social occasions are only warfare concealed."
A 20th century genetically-engineered tyrant who ruled a quarter of the world in the 1990s. As his fellow "supermen" (or augments) were overthrown, Khan and roughly 80 of his followers launched themselves into space in cryogenic sleep before being found by Kirk. With his weakness being his ambition, Khan then tried to seize control of the Enterprise, but failed. Kirk then exiled Khan and his followers to a remote planet where they would build a new society. Unfortunately, not long afterwards, the planet suffered a catastrophic ecological disaster and being completely forgotten by Kirk, Khan grew full of vengeance at the man who cast judgement on him...
Ambiguously Brown: He's a genetically-augmented human from some point in the late 20th century. Most sources cite him having Indian heritage.
Arch-Enemy: More than a hundred years later, Spock would credit him as being "the most dangerous adversary the Enterprise ever faced."
Been There, Shaped History: Given "Space Seed" states Khan lived in the late 20th century and "it's 2001 and Khan wasn't on the cover of People magazine", two novels titled The Rise and Fall of Khan Noonien Singh tries to explain that the Eugenic Wars was some sort of Secret History. Among Khan's achievements are fighting the USSR alongsite Afghanistan, causing a plane crash that killed the leader of the Pakistan's military government, and opening a hole in the ozone layer. (and in a kind of Actor Allusion, his hideout is an island in the French Polynesia)
Bread and Circuses: His ruling style back when he was a dictator over a fourth of Earth, at least compared to his competitors, which was enough to give him a legacy as "the best of tyrants". Notably, there were no massacres under his rule, and he didn't involve himself in the Eugenics Wars until after his territory was attacked. On the other hand, the people under his rule were reduced to subjects with few freedoms.
Rule of Symbolism: Much of the conflict between Kirk and Khan plays out like Paradise Lost, with Kirk as God and Khan as Lucifer. Khan even lampshades this in "Space Seed."
Sealed Evil in a Can: He and his cryogenically frozen followers, in the episode "Space Seed". And again in Star Trek II: The Wrath of Khan, when he's abandoned on Ceti Alpha V (which the crew of the Reliant mistake for Ceti Alpha VI after a natural disaster alters its orbit and destroys its environment).
The main antagonist of "Errand of Mercy" and Kirk's first Klingon opponent. Technically he isn't Star Trek's first Klingon since two troopers are seen before him but he is the primary Klingon in the episode which introduces the race. He returned in one episode of The Animated Series, three episodes of Deep Space Nine (undergoing a Heel-Face Turn with the rest of the Klingons) and more novels and comics than you can shake a stick at.
Affably Evil: Despite intending to execute Kirk once he discovers his identity, he has a drink with him first and is generally hard to dislike.
Not So Different: Kor tries to pull one of these on Kirk, saying they are both warriors on a world of cowards. However, he is horrified when the Organians pull one on him and say one day humans and Klingons will be friends.
The antagonist of "Where No Man Has Gone Before." Mitchell was Kirk's best friend until an accident during a trip to the edge of the galaxy gave him extra-sensory perception and psionic powers, leading him to believe that he was becoming a god.
A God Am I: He frequently refers to himself as such.
Anti-Villain: At first. His initial acts of villainy are simply attempts to stop Kirk and Spock from killing him out of fear for his power. He gradually becomes more evil over the course of the episode and by the end he's left this trope far behind.
Self-Destruct Mechanism: She has one. Kirk activates it twice. The first time, it was a bluff and he calls it off in the nick of time. The second time...
What a Piece of Junk: Over twenty years old by the time Kirk is in command and forty when she's scuttled, but still one of the best ships in the Fleet. Don't call her this and insinuate she's The Alleged Car in front of Scotty however.