As a franchise spanning multiple television series since 1966, Star Trek has brought countless memorable guest stars over the decades. However, not all guest stars are created equal, with several standing as clear highlights in their respective episodes. Whether it’s one-and-done appearances or informal recurring roles, effective guest stars quickly are embraced as fan-favorites. In fact, some connect with the cast, crew, and audience so well, they’ve inadvertently steered the course of the franchise.

A great guest star gels seamlessly with the main cast and naturally elevates the story that they’re appearing in. Rather than simply feeling like stunt casting, a guest role feels like an organic addition to the Star Trek franchise. For the purposes of this article, stars appearing on this list do not include actors who have appeared as series regulars on other Star Trek shows. Here are the 15 best guest stars on Star Trek, ranked in descending order.

Star Trek has had a number of quick cameos over the years, including non-actors playing bit parts on various series and movies. “Star Trek: The Next Generation,” in particular, had several actors and pop culture figures appear throughout its seven-season run, amusingly including Fleetwood Mac drummer Mick Fleetwood as a fish alien. Famed astrophysicist Stephen Hawking went one step further for his cameo on “Star Trek: The Next Generation,” appearing on the Season 6 finale “Descent, Part I.” Rather than play a fictional character, Hawking, a major Star Trek fan, plays a facsimile of himself.

“TNG” regularly featured its main characters playing poker together in their quarters between serving shifts on the bridge. To help improve his poker game, Data (Brent Spiner) programs holograms of Isaac Newton (John Neville), Albert Einstein (Jim Norton), and Hawking to join him for a friendly game. Data’s reasoning is that he would like to study how the greatest scientific minds of all time interact with each other over the game. To his amusement, Hawking fools Einstein into believing he was bluffing in between comparing astronomical observations.

The Star Trek franchise made its triumphant return to television with the launch of “Star Trek: Discovery” in 2017. “Discovery” restored something that had been missing from Star Trek for some time –- salient social commentary, often speaking to contemporary issues through the prism of science fiction. This is never more apparent on the series than the surprise guest-starring appearance of politician and social activist Stacey Abrams on the Season 4 finale. Abrams plays the President of the United Earth, who formally announces the planet is rejoining the United Federation after centuries of strained relations.

So much of the latter half of “Discovery,” set over 900 years after the events of “TOS,” is about rebuilding hope after recovering from catastrophe. Abrams, in her own real-life role with American electoral reform, provides a prominent reminder that there is still much work to do to build a better future. However, just as with her Star Trek character, Abrams points out that this work is meant to be done together as Earth takes its rightful place back in the Federation. Abrams, herself a fan of Star Trek, relished the opportunity to work with the cast and use the show as a platform to instill hope for a better tomorrow.

Jim Kirk (William Shatner) has confronted plenty of Klingons in his time captaining the Enterprise, but his very first Klingon opponent, Commander Kor (John Colicos), is among the most memorable. Appearing on the “Star Trek: The Original Series” episode “Errand of Mercy,” Kor leads the Klingon occupation of the peaceful planet of Organia. As Kirk and Spock (Leonard Nimoy) mount a resistance against Kor and his army, the Klingons escalate their brutality against the Organians. With the Federation and Klingon Empire poised for an all-out war, the Organians reveal their true, all-powerful nature, forming an armistice to Kor’s visible disappointment.

Colicos provides “TOS” with one of its most memorable villains, with Kor meeting every effort made against him in refined viciousness. There is both a palpable animosity and begrudging respect shared between Kirk and Kor, helping establish the Klingons as the most consistent enemy on “TOS.” Nearly 30 years later, Colicos reprised his role as Kor on “Star Trek: Deep Space Nine,” playing an older, embittered version of the Klingon. Appearing on three “DS9” episodes, Colicos cemented Kor’s place as the franchise’s ultimate “TOS”-era Klingon.

By 1992, “The Next Generation” reached the peak of its broadcast popularity, averaging over 11 million viewers per episode. This coincided with Kelsey Grammer becoming a major television star, after a successful run on “Cheers,” and preparing to headline his own spinoff series, “Frasier,” the following year. With both shows produced by Paramount, Grammer was offered the chance to guest star on the “TNG” Season 5 episode, “Cause and Effect.” A Star Trek fan himself, Grammer accepted, appearing as Morgan Bateson, captain of the time-displaced USS Bozeman.

“Cause and Effect” is an episode revolving entirely around strange time-travel mechanics, with the Enterprise and Bozeman trapped in a recurring temporal loop. As such, the two starship crews constantly find themselves living out the same scenes, gradually noticing that something feels off about the situation. In lesser hands, the episode could’ve felt like a repetitive slog, but the cast, including Grammer, and director Jonathan Frakes pull off its execution brilliantly. Grammer, in particular, helps elevate the proceedings, making the confusion the affected crews are experiencing all the more palatable as they try to determine what exactly is going on.

One of the inciting premises behind “Discovery” is the idea that Sarek (James Frain) had an adoptive human daughter in Michael Burnham (Sonequa Martin-Green). The 2nd season of “Discovery” introduces Burnham’s mother, Doctor Gabrielle Burnham (Sonja Sohn), displaced in space and time by a temporal anomaly. Gabrielle reunites with her daughter in the 32nd century after both are flung into the far-future at the end of Season 2. Shaken by her experiences, Gabrielle eventually finds solace in the Ni’Var monastic order, the Qowat Milat.

It’s easy to see where Burnham gets her fiery intensity whenever she shares scenes with mother, with Sonja Sohn bringing the same level of fierce determination as Green. There’s always a lot going on under the surface for the Burnhams, from the lost years as mother and daughter to the galaxy-saving stakes at hand. By the 3rd and 4th seasons, Sohn brings a softer energy in her performance as Gabrielle, no longer scrambling through time to save organic life. Parental dynamics have a special quality in Star Trek especially, and Michael and Gabrielle’s is among the most unique and rewarding.

Harcourt Fenton Mudd (Roger C. Carmel) appears early on “The Original Series,” debuting on the episode “Mudd’s Women” as an interstellar criminal. Carmel reprised his role in the 2nd season episode “I, Mudd,” giving his character a much more comedic approach. Carmel’s final performance as Mudd was on “Star Trek: The Animated Series,” appearing on the 1st season episode “Mudd’s Passion.” Ever the trickster and conman, Mudd was presented more as a nuisance for Kirk and the Enterprise rather than a genuine threat.

Mudd is one of the few recurring characters on “TOS,” with his second appearance actually much more entertaining than his debut. Whereas Carmel initially played Mudd like a conniving crook, his return on “I, Mudd” makes him more of a bumbling buffoon. This portrayal is far better suited to Carmel’s acting strengths and makes “I, Mudd” one of the most outright fun, and funniest, episodes of the series. Though Rainn Wilson does his best playing Mudd on “Star Trek: Discovery,” it never quite reaches the bar originally set by Carmel.

Jane Wyatt memorably played Spock’s mother Amanda Grayson on “The Original Series” and in “Star Trek IV: The Voyage Home,” reminding her son of his rejected humanity. While other actors have played Grayson since, no other actor meets, or arguably exceeds, Wyatt’s performance with the exception of Mia Kirshner. Kirshner plays Grayson on the first two seasons of “Discovery,” providing guidance for Spock (Ethan Peck) and her adoptive daughter Burnham. Kirshner reprises her role as Grayson on “Star Trek: Strange New Worlds,” helping Spock with an engagement event while concealing that he has temporarily been rendered fully human.

Kirshner brings a greater sense of warmth and sympathy to Grayson than any other actor, including Wyatt. Others had played Grayson more distantly, not unlike a Vulcan, despite Grayson embodying Spock’s human heritage. Under Kirshner, Grayson is subtly more open and understanding of her children, especially as Spock faces severe mental instability on “Discovery” Season 2. Kirshner’s return for “Strange New Worlds” gives her a fun and comedic direction to take her character, showcasing her comical chops as she helps Spock with his resurgent humanity.

Before Q, there was Trelane, the omnipotent delinquent played by William Campbell on the “Original Series” Season 1 episode “The Squire of Gothos.” Despite his reality-altering powers, Trelane is presented as an immature figure, infuriated by Kirk’s unwillingness to play his dangerous games. Campbell is a much different adversary for Kirk on the fan-favorite episode “The Trouble with Tribbles,” playing Klingon officer Captain Koloth. Campbell reprised his role as Koloth years later on “Deep Space Nine,” dying honorably in the field of battle on the episode “Blood Oath.”

In lesser hands, Trelane could’ve come off as a character that would be just as annoying to audiences as Kirk and the Enterprise. Under Campbell, the character is playful and mischievous, but fortunately never grating to the viewers. As Koloth, Campbell presents a more light-hearted Klingon antagonist for Kirk, fitting in with the episode’s more comedic sensibilities. Campbell gets the chance to flip this on its head on “DS9,” giving Koloth the final blaze of glory that he so richly deserves.

Captain Kirk has had plenty of love interests on “The Original Series” and subsequent depictions, but one that looms above the rest is Edith Keeler. Played by British actor Joan Collins, Keeler appears on the first season episode “The City on the Edge of Forever.” Keeler lives in 1930 New York City, where she meets a time-traveling Kirk, Spock, and Doctor McCoy (DeForest Kelley) when they travel. Despite the budding romance between Kirk and Keeler, he must allow her death to occur to preserve history and the Prime Timeline.

“The City on the Edge of Forever” is widely regarded as one of the greatest Star Trek episodes, and the episode only works if we believe in Kirk’s love for Keeler. Fortunately, Collins just radiates warmth and grace in her performance, making the audience buy that her character could inadvertently derail the timeline if she was allowed to survive. There is a deep tenderness to Keeler, not only with how she interacts with Kirk, but also how she cares for a gravely ill McCoy. Collins doesn’t just give Star Trek Kirk’s best love interest; she sets a high bar for all guest stars the franchise would see moving forward.

Before he was one of the biggest movie stars in the world, an early acting role for Dwayne Johnson was on “Star Trek: Voyager.” Appearing on the Season 6 episode “Tsunkatse,” Johnson plays a mixed martial arts champion on a planet that the Voyager crew visits on shore leave. After Tuvok (Tim Russ) becomes injured and requires emergency medical attention, Seven of Nine (Jeri Ryan) agrees to face the champion in the ring. During his fights on the episode, Johnson not only does all his own stunts, but delivers some of his signature WWE moves, including the Rock Bottom.

Johnson’s Star Trek role was at the arguable peak of his professional wrestling career and a full year before his big-screen debut in “The Mummy Returns.” Johnson leans into many of his usual wrestling heel tricks of the trade, gamely grandstanding for the audience with all of his star-making swagger. This role elevates “Tsunkatse” to be one of most memorable episodes of “Voyager,” particularly in the show’s later years.

Mark Lenard has the rare distinction of not only playing multiple Star Trek characters, but also getting to play a Romulan, Vulcan, and Klingon in his time with the franchise. Lenard’s association with Star Trek began by playing a cunning Romulan commander in the “Original Series” 1st season episode “Balance of Terror.” Lenard’s most iconic Star Trek role came the following season, playing Spock’s father Sarek, a role he reprised on “The Animated Series,” several movies, and “The Next Generation.” In addition to his television roles, Lenard also played an ill-fated Klingon commander in 1979’s “Star Trek: The Motion Picture,” completing his trifecta of Star Trek aliens.

Exuding gravitas whenever he’s on-screen, Lenard brings a sort of classic thespian presence to Star Trek, especially in its early years. As either a Romulan or a Vulcan, Lenard conveys so much emotion despite the visibly staid demeanor that both races are known for. Sarek’s scenes with Spock are among the best Leonard Nimoy has ever played as his most iconic role, with the two actors bringing out their best in each other. Similarly, Lenard’s final appearances as Sarek on “TNG” are utterly heartbreaking, showing the tragic end of a great man.

By the time David Warner appeared for his guest-starring role on “The Next Generation,” he had already played two different characters in separate Star Trek movies. After playing a human in 1989’s “Star Trek V: The Final Frontier” and a Klingon in 1991’s “Star Trek VI: The Undiscovered Country,” Warner played a Cardassian on “TNG.” Warner’s sadistic Gul Madred appears on the Season 6 two-parter “Chain of Command,” who captures and tortures Jean-Luc Picard (Patrick Stewart). Madred torments Picard, intent on breaking his spirit, nearly succeeding in doing so until Picard’s timely release.

Of all the on-screen adversaries Picard has faced over the years, few match him in dignity and gravitas as Warner’s Madred. For as noble and magnanimous as Picard is, Madred is wickedly cunning and devious, relishing in punishing Picard in exceedingly grueling ways. Stewart and Warner had first collaborated together in a ’60s British stage production of Hamlet, maintaining a mutual respect for each other. This significantly enhances their performance together on “TNG,” giving Picard and Madred’s brutal dynamic an engagingly refined air.

When the Borg debuted on “The Next Generation,” they appeared as a true collective, with no clear individual leader for them to rally behind. 1996’s “Star Trek: First Contact” introduced the Borg Queen, the singular entity leading the Borg as they mounted a time-bending attack on Earth. Played by Alice Krige, the Borg Queen survives her defeat in “First Contact,” reappearing in a guest-starring capacity on the two-part “Voyager” series finale. After a brief return on “Star Trek: Lower Decks,” Krige reprised her role in a greater capacity on “Star Trek: Picard” as the final season’s overarching villain. For “Picard,” Krige voiced the character while Jane Edwina Seymour served as her body double.

The Borg was quickly established as the ultimate “TNG” enemy, with the stakes raised immeasurably whenever they surfaced. With Krige as the Borg Queen, the Borg gained a figurehead to rally around and a sneering face to Picard and Seven of Nine’s deep-seated trauma. “Voyager” had defanged the threat of the Borg somewhat, but Krige’s return as the Queen reinforced that sense of danger, something that Krige improves upon on “Picard.” The one adversary that can consistently rattle the normally stoic Picard and Seven of Nine to their core, Krige’s Borg Queen is an enemy for the ages.

The very first antagonist Picard and the crew of the Enterprise face in “The Next Generation” isn’t the Borg, the Klingons, or the Romulans, but Q. Played by John de Lancie, Q appears on the two-part “TNG” series premiere, declaring himself an omnipotent judge observing humanity. Selecting Picard as humanity’s representative, Q threatens to use his reality-shaping powers to erase the species’ existence if he deems them unworthy. Beyond the premiere, Q would reappear at least once each season of “TNG,” culminating in him returning to his judge role in the two-part series finale.

Star Trek keeps bringing back de Lancie as Q because he’s so effectively compelling to watch, with the character alternating between adversary and ally on a whim. This distinction goes beyond “TNG,” with de Lancie reprising his role as Q on “Deep Space Nine,” “Voyager,” “Picard,” and “Lower Decks.” Q’s motives and methodology vary in each appearance, sometimes playing as a mischievous trickster and sometimes as a genuine menace. Q’s flexibility as a character not only speaks to de Lancie’s prodigious acting but also the inherent malleability of Star Trek personified.

Originally appearing as a one-off villain on the “Original Series” Season 1 episode “Space Seed,” Ricardo Montalbán played the formidable Khan Noonien Singh. A genetically enhanced despot from the late 20th century, Khan and his followers were exiled into deep space before being discovered by the Enterprise centuries later. Kirk is barely able to defeat the revived Khan, marooning him and his people on a remote planet. Montalbán went on to reprise his role as Khan in 1982’s “Star Trek II: The Wrath of Khan,” cementing his villainous dynamic with Kirk and revitalizing the wider franchise.

In case there is any doubt regarding Montalbán’s esteemed guest-star status, his one-episode appearance was enough to inspire an entire movie featuring his return. No other actor throughout Star Trek history can stake that claim of being elevated to a primary movie villain after a single guest-star role. Thematically, if Star Trek depicts enlightened humanity as a post-scarcity utopia, Khan represents the sinister potential that the future can yield. That effectiveness is sealed by Montalbán’s performance, magnetic whenever he’s on-screen and, like his character, as physically imposing as he is eloquent and graceful.