Several characters within the Star Trek franchise, primary and secondary, often made crossover appearances between one series and another. This included appearances of established characters on premiere episodes of new series, a few long-term transfers from one series to another, and even crossovers between Trek films and television. A few crossover appearances, such as that of Spock on The Next Generation and the time-travel of the crew of Deep Space Nine to the era of The Original Series were especially lauded by both fans and critics.
Appearances in series premieres
After The Original Series, at least one character from an earlier series appeared in the premiere episode of each new series. These were the appearances of most of the Original Series main cast in "Beyond the Farthest Star", the first episode of The Animated Series; Leonard McCoy in "Encounter at Farpoint", the first episode of The Next Generation; Captain Jean-Luc Picard and Miles O'Brien in "Emissary", the first episode of Deep Space Nine; Quark and Morn in "Caretaker", the premiere of Voyager; Zefram Cochrane (from the original series episode "Metamorphosis" and the film Star Trek: First Contact) in "Broken Bow", the premiere of Enterprise; Sarek in "The Vulcan Hello", the first episode of Discovery; Sylvia Tilly in "Runaway", the first episode of Short Treks; Jean-Luc Picard and Data in "Remembrance", the first episode of Picard; NOMAD (from the original series episode "The Changeling") in "Second Contact", the premiere of Lower Decks, a training hologram resembling Captain Katherine Janeway in "Lost and Found, Part 1", the first episode of Prodigy, and Captain Christopher Pike, Spock, Una, Christine Chapel, Nyota Uhura, Joseph M'Benga, Robert April, T'Pring, and George Samuel Kirk in "Strange New Worlds", the premiere of Strange New Worlds.
Two long-term transitions were the transfer of Worf and Miles O'Brien from permanent characters on The Next Generation to permanent characters on Deep Space Nine. Worf stayed on The Next Generation until its conclusion, then transferred from the start of season 4 of DS9. Chief O'Brien had appeared in fifty episodes of The Next Generation, but only gained opening credits billing on DS9, in which he appeared in almost every episode of all seven seasons. While not seen as often as Chief O'Brien, his wife Keiko O'Brien also transitioned as a series regular guest star from The Next Generation to Deep Space Nine, bringing their daughter Molly. Miles O'Brien reprised his Next Generation role in that series' finale "All Good Things...".
Episodes and films focused on crossovers
An especially significant crossover is Spock's appearance on the two-part Next Generation episode "Unification". Spock meets Data and they exchange opinions on the relative value of logic and emotion, and share mutual impressions of Next Generation's Captain Picard (who for Spock is a model of logical behavior, and for Data is a model of what it means to be human). Critics such as Ina Rae Hark have noted this encounter between two non-human characters in which they summarize their contrasting attitudes to humanity, Data embodying Spock's ideal of pure logic, while Data aspires to be more human.
Scotty appears in TNG Season 6, Episode 4 "Relics".
Recycled footage from the original series episode "The Trouble with Tribbles" is used extensively in Deep Space Nine's time-travel episode "Trials and Tribble-ations". In addition to extensive archival footage of cast from the original series, actor Charlie Brill (portraying Klingon spy Arne Darvin) appears in both new and archival footage. The episode was designed to coincide with the 30th anniversary of the original series. Critic Matthew Kappell notes that the new episode simultaneously "parodies and valorizes" the original series, highlighting the discontinuities between two eras of Trek while trying simultaneously to weave them together.
William Riker and Deanna Troi from The Next Generation appear in a flash-forward to the future in "These Are the Voyages...", the final episode of Enterprise. This episode was widely criticized by both cast members and fans for playing more like a Next Generation episode to the point of being an inappropriate wrap-up for the series.
Strange New Worlds episode "Those Old Scientists" features live-action appearances of Beckett Mariner and Brad Boimler from the animated Lower Decks series.
In the Voyager episode "Flashback", events from the film Star Trek VI: The Undiscovered Country (1991) play a pivotal role, and are reenacted with the same actors, thus allowing George Takei to reprise his role as Hikaru Sulu. The episode contains the added revelation that the character of Tuvok was on Sulu's ship Excelsior at the time. Critic Lincoln Geraghty cites this as an example of Star Trek's ongoing propensity for reverential recognition of earlier versions of the series. In bit of rather glaring discontinuity, the character of Lieutenant Dimitri Valtane is shown to be both alive at the end of the film and dead in the episode. Actor Tim Russ, who portrayed Tuvok, also made an appearance as a bridge officer from the same fictional time period, serving on the Enterprise-B in the feature film Star Trek Generations (1994).
The film Star Trek Generations brought Kirk and Picard, Enterprise captains from different centuries, together to defeat a common enemy. It also marked the passing of the film franchise from the original series cast to that of The Next Generation.
Characters more prominent on subsequent series
A few occasional recurring characters introduced in one series continued into other series, sometimes attaining more significant roles in their subsequent Trek series than in the one in which they were first introduced:
- Spock's father Sarek appeared in only one episode of the original series, but became a more developed character in three movies and appeared in the Next Generation episode named after him and the first part of "Unification". Sarek's appearance in the former is described in The Star Trek: The Next Generation Companion as "the first major unifying event tying together the old and new Trek eras since McCoy's cameo" in the original series. Sarek later appeared in Star Trek: Discovery.
- Recurring character Q, originally introduced in the premiere episode of Next Generation, continued to appear in episodes of Deep Space Nine, Voyager, Lower Decks and Picard. Teleplay writer Robert Wolfe found it difficult to incorporate Q into the DS9 universe as the character had been conceived so much as a foil for Captain Picard. He eventually decided to use Q to show personality differences between Picard and Sisko. It was also difficult to decide how to introduce Q into Voyager, as it was necessary to explain why Q did not return the ship to Federation territory.
- Although appearing in only five episodes of The Next Generation and six episodes of Voyager, the character of Reginald Barclay became quite pivotal to the story-arc of the final season of Voyager, significantly contributing to the reestablishment of contact between the ship Voyager and the Federation. Barclay also appears in a cameo role in the eighth movie in the film series, Star Trek: First Contact.
- Three Klingon characters from separate individual episodes of the original series, Kor, Koloth and Kang, all appear in the Deep Space Nine episode "Blood Oath", and Kor further appeared in DS9 episodes "The Sword of Kahless" and "Once More Unto the Breach". Crew members who worked on "Blood Oath" felt that a "special connection" was being made to the original series. Kang made an additional cameo appearance on Voyager, verbally dueling with Captain Sulu in a brief scene of the episode "Flashback".
- The two Ferengi, Arridor and Kol, were minor characters in the TNG episode "The Price" but were the principal antagonists in the Voyager episode "False Profits".
- The Borg race appeared in five of the Star Trek series. Introduced in The Next Generation, they would appear in Deep Space Nine, Voyager, Enterprise, and Picard. Their role in Deep Space Nine was limited to an appearance in the premiere episode to explore Benjamin Sisko's troubled past (his wife having been killed in a major confrontation with the Borg), while their role in the Enterprise episode "Regeneration" served as a 'sequel' to Star Trek: First Contact, as an archaeological expedition discovers the remains of the time-travelling Borg sphere that was destroyed in First Contact and unwittingly reactivate a pair of Borg drones. However, the Borg became a recurring threat on Voyager. One crossover character was the Borg Queen first introduced in the Next Generation feature film Star Trek: First Contact. She would then become a recurring character on Voyager appearing in the two-part episodes "Dark Frontier" and "Unimatrix Zero" and in the series finale "Endgame". These episodes form a narrative thread in which the Borg Queen is battling with Janeway in attempts to re-assimilate Seven of Nine. Only in the final Voyager episode is the Borg Queen played by the same actress who played her in the feature film Star Trek: First Contact, Alice Krige. The magazine Cinefantastique described Krige's appearance as the highlight of this episode. Eventually a new, cloaked form of the Borg Queen appears in Star Trek: Picard, quickly followed by a version more reminiscent of the appearance and personality of the character seen in First Contact and Voyager, in an alternate timeline. Another crossover character is Hugh, a Borg drone who appeared in the TNG episode I, Borg and subsequently in the first season of Picard.
- The Original Series on The Animated Series
- The Original Series on The Next Generation
The Original Series on The Next Generation series of films
- The Original Series on Deep Space Nine
- Kang, Koloth, and Kor (with their cranial ridges "restored") appear in "Blood Oath". Kor appears subsequently in "The Sword of Kahless" and "Once More Unto The Breach".
- James T. Kirk, Spock, Leonard McCoy, Montgomery Scott, Pavel Chekov, Nyota Uhura, Cyrano Jones, and Korax appear in "Trials and Tribble-ations" (There were clips from the Star Trek: The Original Series episode "The Trouble with Tribbles ", but Benjamin Sisko 's conversation with James T. Kirk was based on footage taken from the episode "Mirror, Mirror").
- The Original Series on Voyager
The Original Series on Enterprise
The Original Series on Star Trek (2009), Star Trek Into Darkness (2013), Star Trek: Beyond (2016)
- Aside from a complete recasting of all the primary roles from the original series, the reboot Star Trek film series also specifically brought back Leonard Nimoy to reprise his role as Spock last seen in the Next Generation two-part episode Reunification for the first two films in the reboot series. A recast Sarek, a recasting of Spock's mother Amanda (Winona Ryder), and a recast Captain Pike also appears in Star Trek (2009).
- Pike and Ambassador Spock (Nimoy) reappear in Star Trek Into Darkness (2013) alongside a recast Khan Noonian Singh and Doctor Carol Marcus, characters who were last seen in Star Trek II: The Wrath of Khan.
- Nimoy's Ambassador Spock, and the rest of the original series cast reappear in holographic (Spock) and photographic form in Star Trek: Beyond (2016) and have no speaking roles.
- The Original Series on Discovery
- The characters Sarek, Amanda Grayson, Spock, Christopher Pike, Number One and Harry Mudd from The Original Series appear as recurring characters in Discovery, all played by different actors. The Talosians and Vina, from the unaired pilot of the original series "The Cage" and the two-part original series episode "The Menagerie," also appeared in the Discovery episode "If Memory Serves". Archival footage from "The Cage" was also used in "If Memory Serves", with archive footage of Leonard Nimoy as Spock from the episode "Unification II" being used in the Discovery episode "Unification III"
- The Guardian of Forever appears in both parts of the episode "Terra Firma", though it is only revealed to be the Guardian in the second part. The character last appeared in "Yesteryear", an episode of The Animated Series.
The Original Series on Short Treks
- The Original Series on Lower Decks
- NOMAD (from the original series episode "The Changeling") appears in a storage room in "Second Contact"
- The characters Spock and James T. Kirk are depicted in their Animated Series form for a brief, mute cameo in the first season finale "No Small Parts", with Landru from "Return of the Archons" also making a brief appearance.
- The Next Generation on Deep Space Nine
- Captain Jean-Luc Picard appears in the episode "Emissary"
- Miles O'Brien, Keiko O'Brien, and Worf make long term moves to the station, starting with "Emissary", "A Man Alone", and "The Way of the Warrior", respectively.
- Lursa and B'Etor appear in the episode "Past Prologue"
- Vash appears (with Q) in the episode "Q-Less"
- Lwaxana Troi appears in the episodes "The Forsaken", "Fascination" and "The Muse"
- Fleet Admiral Alynna Nechayev appears in the episodes "The Maquis, Part II" and "The Search, Part II"
- Gowron appears on numerous episodes, starting with The House of Quark.
- Thomas Riker appears in the episode "Defiant"
- Toral the illegitimate nephew of Lursa and B'Etor appears on the episode "The Sword of Kahless"
- Kurn brother of Worf appears in the episode "Sons of Mogh"
- Alexander Rozhenko appears in the episodes "Sons and Daughters" and "You Are Cordially Invited"
- The Next Generation on Voyager
- The Next Generation on Enterprise
- The Next Generation on Short Treks
- The Next Generation on Picard
- The Next Generation on Lower Decks
- Q appears in the episode "Veritas"
- William Riker and Deanna Troi appear in the first season finale "No Small Parts"
- A holographic statue of Miles O'Brien appears in the far future in the episode "Temporal Edict"
- Deep Space Nine on The Next Generation
- Deep Space Nine on Voyager
- Deep Space Nine on Lower Decks
- Voyager on The Next Generation series of films
- The Mark I EMH "Doctor" appeared in the film Star Trek: First Contact. This EMH, while identical in name, appearance and mannerisms, was distinct from the Voyager character due to the nature of the EMH being a holographic computer program.
- Vice Admiral Kathryn Janeway has a brief cameo in the film Star Trek: Nemesis
- Voyager on Deep Space Nine
- Voyager on Picard
- Seven of Nine has appeared five times in the first season episodes of Star Trek: Picard : "Absolute Candor", "Broken Pieces", "Et in Arcadia Ego: Part I", "Et in Arcadia Ego: Part II" and in "Stardust City Rag" she appears alongside Icheb in a final and brief cameo role. Icheb however is portrayed by different actors than those who had acted in the role on Star Trek: Voyager.
- Discovery on Short Treks
- The characters of Tilly and Saru appear in the episodes "Runaway" and "The Brightest Star" respectively, with Phillipa Georgiou also appearing briefly in the latter episode
- Younger versions of Michael Burnham and her father Mike Burnham appear in the animated episode "The Girl Who Made The Stars"
- Short Treks on Discovery
- Me Hani Ika Hali Ka Po from the Short Treks episode "Runaway" appears in both parts of the Discovery episode "Such Sweet Sorrow"
- Siranna from the Short Treks episode "The Brightest Star" appears in the Discovery episodes "The Sound of Thunder", "Such Sweet Sorrow, Part 2" and through archival footage in "Lights and Shadows"
- The Original Series on The Next Generation
The Original Series on The Next Generation, Deep Space Nine and Voyager:
The Original Series on Deep Space Nine:
Clint Howard who played Balok on the episode “The Corbomite Maneuver” appeared as the mentally ill Sanctuary resident Grady in DS9’s “Past Tense, Part II”
The Original Series on Enterprise:
Clint Howard who played Balok on the episode “The Corbomite Maneuver” played the ferengi Muk in Enterprise’s first-year episode “Acquisition”
The Original Series on Discovery:
Clint Howard who played Balok on the episode “The Corbomite Maneuver” played an Orion Drug Dealer in the Star Trek: Discovery season one finale, "Will You Take My Hand?"
- The Next Generation on The Original Series
- The Next Generation on Deep Space Nine
- Marc Alaimo (Cmdr. Tebok / Gul Macet / Frederick LaRouque) plays a major role as the Cardassian military officer, Gul Dukat.
- Deep Space Nine on The Original Series
- Rene Auberjonois (Odo) also appears as Colonel West, a human assassin disguised as a Klingon intent on assassinating the Klingon Chancellor at the Khitomer Conference.
- Voyager on Deep Space Nine
- Voyager on The Next Generation
- The Next Generation on Enterprise
- Enterprise on Voyager
- Deep Space Nine on Voyager
- Deep Space Nine on Enterprise
- Voyager on Enterprise
Star Trek has had a few intercompany crossover stories in comic books. These include:
Marvel Comics franchise, X-Men
DC Comics franchise, Legion of Super-Heroes
- Star Trek – Legion of Super-Heroes
IDW Publishing, Doctor Who
Boom! Studios, Planet of the Apes
DC Comics franchise, Green Lantern
Dark Horse Comics, Alien
- Star Trek: The Next Generation/Aliens: Acceptable Losses (cancelled)
IDW Publishing, Transformers
(Star Trek – Legion of Super-Heroes also reveals that DC's Vandal Savage and Flint, a mysterious immortal encountered by James T. Kirk and his crew, are actually parallel universe versions of the same person. While one version adopted the name Vandal Savage and dedicated himself to conquest, the other version adopted the name Flint and turned his life towards art and science.)
CCG intercompany crossover scenario
Lucasfilm franchise, Star Wars
In Turkish comedy Turist Ömer Uzay Yolunda (Turkish: Ömer the Tourist in Star Trek), produced and directed by Hulki Saner, titular hobo (cult turkish character, Turist Ömer played by Sadri Alışık) is beamed aboard the Starship Enterprise.
In Polish cabaret sketch of Kabaret Moralnego Niepokoju (Polish: Cabaret of Moral Anxiety) - Bajki: Przygody pilota Pirxa, titular hero (taken from Stanisław Lem Tales of Pirx the Pilot), and his companions, wears TNG era Starfleet uniforms. Star Trek style technobabble is also in use.