Star Trek: The Original Series has featured some memorable guest stars alongside its iconic regular cast.
It was rare that an episode of Star Trek didn't feature any guest stars: only two episodes -- "The Immunity Syndrome" and "The Tholian Web" -- come to mind offhand as having no featured guest players in addition to the show's main stars and assorted supporting cast. And while some of those guest stars ranged from colorful if not particularly memorable aliens to generic Federation bureaucrats -- anyone remember Commodore Stocker? -- Star Trek in its three seasons also unveiled a surprisingly strong gallery of exceptional guest stars who graced the show with striking performances, ingenious characters or both.
Here then is a list of the 17 best guest stars -- hero or villain -- to ever hitch a ride on, attempt to hijack, threaten to destroy or capture as a plaything the U.S.S. Enterprise and provide its crew with that week's measure of excitement, terror or romance. They're all in their own way as beloved to Trekkers as Kirk, Spock, Bones and the rest of the gang...
17. Celia Lovsky as T'Pau ("Amok Time")
"All of Vulcan in one package" is how Captain Kirk describes the Vulcan priestess T'Pau, who presides over the wedding ceremony of Spock and his intended bride, T'Pring, in the classic episode that explores the strange mating rituals of Vulcans. Kirk is surprised to see T'Pau -- "the only person to turn down a seat on the Federation Council" -- at Spock's ceremony, and it's partially her presence there that makes Kirk not back down when asked to participate. As played by the Austrian-American Lovsky, T'Pau is regal, mysterious, intelligent and emotionless, but not devoid of compassion. In other words, all of Vulcan in one package. Fun fact: Lovsky's final film role was in the 1973 sci-fi classic Soylent Green.
16. Ted Cassidy as Ruk ("What Are Little Girls Made Of?")
This early episode, in which Kirk and Nurse Chapel discover an old lover of Chapel's using the technology of an extinct alien civilization to create a race of androids, is memorable for many reasons, including the fact that it was penned by Robert Bloch and featured Sherry Jackson as perhaps the sexiest android to ever grace the screen until Tricia Helfer played a Cylon. But the single best aspect of the show is Ted Cassidy -- best known as Lurch on The Addams Family -- as the bald, seven-foot-tall behemoth of a robot left behind by the "Old Ones." Cassidy's formidable physical presence, his deep voice and terrific makeup job made Ruk one of Trek's best monsters. Fun fact: Cassidy also did the voice for the "scary" version of Balok in the ST: TOS episode "The Corbomite Maneuver" and the Gorn in "Arena."
15. Jill Ireland as Leila Kalomi ("This Side of Paradise")
Even with a woman as clearly in love with him as Leila Kalomi around, it would still take the intervention of alien spores to finally break down Mr. Spock's logical defenses so that he allowed himself to love Leila back. That's exactly what happens in this acclaimed episode, in which the crew of the Enterprise is brought to its knees by a bout of unbridled happiness (courtesy of those crazy plants, of course). Ireland is tender and poignant as Leila, who finds a way to finally get Spock to reciprocate her unrequited love. Their scenes together are moving, funny and finally heartbreaking. Ireland went on to make many films with her husband, Charles Bronson, before her untimely death from cancer at age 54.
14. William Marshall as Dr. Richard Daystrom ("The Ultimate Computer")
With his booming voice and intimidating height (six-foot-five), William Marshall was a powerful presence and more than appropriate for the role of Dr. Daystrom, the brilliant yet erratic scientist who has designed the computer aboard the Enterprise and now uses the ship to test his newest creation, the M-5. But when the powerful M-5 begins to show signs of unstable behavior itself -- the result of its creator using his own brain engrams for the device -- inventor and machine both start losing their minds. Marshall is intense and alarming as Daystrom, gradually going mad from pride and megalomania, and his tortured performance makes Daystrom one of Trek's best anti-heroes. Fun fact: Marshall went to become a horror icon by playing the title vampire in the classic blaxploitation chillers Blacula (1972) and Scream Blacula Scream (1973).
13. John Colicos as Kor ("Errand of Mercy")
March 23, 1967. That was the date on which this classic episode was first broadcast and we got our initial look at the Klingons, who would go on to become the chief enemies of the Federation and Captain Kirk. They were embodied in this episode by Kor, the ruthless and cunning Klingon commander who conquers the entire planet of Organia (or so he thinks) only to find that he hungers for someone, anyone on the seemingly docile world to fight back. Kor is a military creature through and through, but even he sees sense when the Organians reveal their true nature. Fun fact: The crafty Colicos was so good in the role that he was asked back to reprise it many years later on Deep Space Nine.
12. Clint Howard as Balok ("The Corbomite Maneuver")
One of the best Star Trek episodes to emphasize the show's themes of exploration and understanding, "The Corbomite Maneuver" also boasts one of its most surreal aliens. After tricking the Enterprise crew with a transmission of a fright-mask meant to be himself, Commander Balok finally reveals his true form to Captain Kirk and a landing party -- and turns to be a lot less intimidating in person. Seven-year-old Clint Howard played the tiny Balok with his voice dubbed by an adult male, and the result was a being who taught us, in the best Trek tradition, that appearances can be deceiving. Fun fact: Howard is the younger brother of actor-turned-director Ron Howard and has shown up in nearly all his movies.
11. Gary Lockwood as Gary Mitchell ("Where No Man Has Gone Before")
Two years before he would journey to Jupiter in Stanley Kubrick's ground-breaking 2001: A Space Odyssey, Gary Lockwood signed on to play the navigator of the Enterprise -- and best friend of James T. Kirk -- in the second Star Trek pilot commissioned by NBC. The story follows the Enterprise to the rim of the galaxy, where an energy barrier zaps Lockwood's Lieutenant Mitchell and ship psychiatrist Elizabeth Dehner (Sally Kellerman), turning them into godlike beings with unlimited powers. As Mitchell becomes more dangerous, Kirk must decide whether or not he can kill his friend. Initially rogueish and charming like Kirk himself, Lockwood effectively portrays Mitchell's chilling transformation, aided by those eerie silver eyes. Fun fact: Lockwood played the title role in Star Trek creator Gene Roddenberry's first produced series, The Lieutenant, which lasted one season.
10. Frank Gorshin as Bele and Lou Antonio as Lokai ("Let That Be Your Last Battlefield")
Star Trek's third season did not yield up a lot of quality episodes, but the show was on point with this sharp if heavy-handed allegory on racism. Gorshin and Antonio are the last survivors of the planet Cheron, whose hatred for each other's races -- and each other -- eclipses the sad reality that they are all that is left of their people. That one is black on the left side and the other on the right only renders their hate more meaningless. Gorshin, best known as the Riddler on the 1960s Batman series, makes an especially memorable impression here in a serious role. Fun fact: Speaking of impressions, Gorshin was an amazing impressionist and the first one to ever headline all the showrooms of the main hotels in Las Vegas.
9. Michael Ansara as Kang ("Day of the Dove")
As one of the original series' great Klingon commanders, Michael Ansara was, like John Colicos and William Campbell (Koloth in "The Trouble with Tribbles") invited to reprise his role on Deep Space Nine. Like Kor from "Errand of Mercy," Kang relishes the idea of hand-to-hand, take-no-prisoners battle with the crew of the Enterprise, although like our heroes, he doesn't realize that the whole thing is being engineered by an entity that feeds on violent emotions. When the truth is finally revealed, he does the sensible thing and lays down his arms -- for as he says, only a fool fights in a burning house. Ansara's layered performance gives us the first glimpse of the vaunted Klingon honor that would feature in later series. Fun fact: Ansara is one of nine actors to play the same character on three different Star Trek TV series, with Kang showing up in the Deep Space Nine episode "Blood Oath" and the Voyager segment "Flashback" in addition to "Day of the Dove."
8. Mark Lenard as the Romulan Commander ("Balance of Terror")
One of several Star Trek guest players to be invited back in another role -- which we'll get to shortly -- Mark Lenard made his first striking appearance on the show in this classic cat-and-mouse game between the Enterprise and a Romulan ship on the edge of the Neutral Zone, where one wrong move could spiral into a destructive galactic war. Lenard's Romulan Commander is thoughtful yet decisive, a seasoned warrior who is nevertheless weary of war, and as the show progresses he and Kirk both develop a growing admiration and understanding for each other. Fun fact: Lenard also played the gorilla general Urko in the short-lived 1974 Planet of the Apes TV series.
7. Roger C. Carmel as Harry Mudd ("Mudd's Women"/"I, Mudd")
Everyone's favorite space pirate and con man, Harry Mudd made his debut in the sixth Star Trek episode ever broadcast, as the dubious shepherd guiding his flock of medically-enhanced women to lonely workers at a distant mining colony. While "Mudd's Women" was a relatively restrained episode, Mudd returned in Season Two in the much wackier "I, Mudd," in which Harry finds himself both prisoner and ruler of a planet of androids. Roger C. Carmel played the slippery snake oil salesman in more sober fashion in the first episode but displayed his range in the second, one of Trek's few out-and-out comedies. Although never a serious threat, Harry's penchant for bringing chaos in his wake bedeviled the orderly, buttoned-up captain of the Enterprise. Fun fact: a third Mudd episode was in development at one time for the show's third season, but ended up on the animated series instead ("Mudd's Passion").
6. Robert Walker Jr. as Charles Evans ("Charlie X")
When 17-year-old Charles Evans is rescued from the planet Thasus, having seemingly survived there on his own without anyone else, Kirk, Spock and McCoy are understandably suspicious. Their suspicions are borne out when it becomes apparent that Charlie did have help of some kind -- the kind of help that gives a young boy an incredible power to manipulate matter. But awkward, lovestruck Charlie doesn't know how to rein his powers in and find his place in society again. Robert Walker Jr. gives an earnest and ultimately heartbreaking performance in an early standout for the series. Fun fact: Gene Roddenberry made an uncredited audio cameo as the mess officer who informs Kirk that the meatloaf in the ship's kitchen's ovens has turned into real turkeys.
5. William Campbell as Trelane ("The Squire of Gothos")
Like Charlie Evans, Trelane -- "the lonely squire of Gothos" -- possesses immense powers but doesn't have the emotional or intellectual capacity to use them properly. You see, Trelane is nothing but a small child, and he captures the crew of the Enterprise for use as his playthings --- that is, until his parents show up and tell him it's time to come in. William Campbell, who we mentioned above for his stint as Koloth, became one of Trek's most popular guest stars with his enduring turn as the haughty, arrogant and bratty Trelane. His devolution from omniscient menace to whimpering crybaby is a sight to behold. Fun fact: Campbell starred in Francis Ford Coppola's first official film as a director, the low-budget 1963 horror flick Dementia 13.
4. William Windom as Commodore Matt Decker ("The Doomsday Machine")
William Windom perhaps never got his due as a character actor, but his appearance as the captain of the doomed U.S.S. Constellation on a Ahab-like quest to destroy a planet-killing robot remains a high point of his career. Windom does chew the scenery a bit, but he and Leonard Nimoy create a real sense of tension as they wrestle for control of the Enterprise bridge after Decker pulls rank and takes command while Kirk ia away. Decker is one of Trek's most tragic characters, losing his crew, his ship, his mind and finally his life in a futile effort to thwart the giant weapon. Fun fact: Windom later played the President of the United States in 1971's Escape from the Planet of the Apes.
3. Mark Lenard as Sarek and Jane Wyatt as Amanda ("Journey to Babel")
Many of Trek's best episodes took deep dives into the character of Mr. Spock, and perhaps the finest was this gem in which we are introduced to his mother and father and learn why dad and son have not spoken for years. Mark Lenard returns to the show with a sensitive and subtle performance as Sarek (a character he would play several more times in the movies and on The Next Generation), while Wyatt is properly emotional and anguished as his wife. The scene in which Amanda confronts her son in his quarters features some of Nimoy's very best work as Spock, by the way. Fun fact: Mark Lenard also showed up as a Klingon commander in Star Trek: The Motion Picture, making him the only actor to play a character from all three of the show's major alien races.
2. Joan Collins as Edith Keeler ("The City on the Edge of Forever")
When Kirk and Spock travel through a gateway in time to Depression-era New York, where they must find a drug-addled McCoy before he accidentally changes history, Kirk finds himself drawn to the ethereal, compassionate "street angel" Edith Keeler, who runs a mission and talks of mankind one day traveling peacefully to the stars. The two fall deeply in love, but Kirk learns to his horror that it is Edith's death that must occur in order for history to be restored. "City" is frequently cited as the best Star Trek episode ever made, and with good reason: it's an epic, moving science fiction story, and Joan Collins -- in her pre-Dynasty days -- is marvelous and beautiful as Kirk's doomed love. Fun fact: Joan Collins was already a well-known actress when she appeared on Star Trek -- a job she took after her oldest daughter expressed excitement about her mom possibly guesting on the show.
1. Ricardo Montalban as Khan Noonien Singh ("Space Seed")
At its best, Star Trek was a show about ideas, but when the series rolled out a full-on villain, it could really hit them out of the park too. Khan, the genetic superman from the past who is revived and decides he wants to rule the future, remains the greatest Trek antagonist of them all, a powerful would-be tyrant whose strength is matched only by his intelligence and calculating nature. Ricardo Montalban was perfection in the role, bringing a seductive flair to the part while at the same time looking like he could kick Kirk's butt really bad. It's no wonder that he returned for Star Trek II: The Wrath of Khan -- still the gold standard of Trek on the big screen -- and luckily the ill-conceived reboot of the character in Star Trek Into Darkness has not damaged the reputation of the original. Fun fact: Montalban was also a veteran of the Apes franchise, playing circus owner Armando in 1971's Escape from the Planet of the Apes and 1972's Conquest of the Planet of the Apes.