Star Trek is full of one-off characters, species, planets, and technologies — unsurprising, considering how sprawling the franchise has become. But every once in a while, a seemingly-forgotten concept resurfaces. Series creators use these ideas not just for nostalgia, but to pick up story threads that were dropped long ago, tying old and new media together. One such concept made a reappearance in Season 3 of Star Trek: Discovery, after almost 50 years.

In season 3, episodes 9 and 10, "Terra Firma," Star Trek audiences were reunited with the Guardian of Forever. This strange being and/or device first appeared in The Original Series season 1, episode 28, "The City on the Edge of Forever." Though it's not the central focus of either story, the Guardian of Forever is an intriguing mystery for fans both old and new. Who or what is it, and what do we know about it?

The Guardian in The Original Series

In "The City on the Edge of Forever," the Enterprise crew is investigating a temporal disturbance when Dr. McCoy accidentally injects himself with an overdose of a dangerous drug. In a frenzy, he beams himself down to the planet they are orbiting, forcing the crew to chase him. On the planet's surface, the crew finds a strange gate, glowing with a strange light. Upon scanning it, Spock realizes that it is the source of the temporal anomalies. Kirk asks whether the structure is a being or a machine. It responds, speaking as it pulses with light:

Through the gate, Kirk and the rest see Earth's history flashing by. As they watch, McCoy's madness overtakes him, and he runs through the portal. As soon as he does, the ship disappears and the crew is left stranded — whatever McCoy did, he changed history, and it's up to Kirk, Spock, and the Guardian to set it right. With the Guardian's help, Kirk and Spock estimate the point in time where McCoy might have ended up, and follow him to 1930s Earth.

"The City on the Edge of Forever" is widely considered one of the best episodes of TOS, and is worth watching unspoiled. It explores fascinating sci-fi questions, speculating on the nature and consequences of time travel. At the same time, it's one of the series' most emotionally resonant stories. As he and Spock navigate their unfamiliar surroundings, Kirk's greatest strengths and biggest flaws are both on display. He's torn between duty and compassion as his friend, the world's future, and the woman he's falling for are all in danger. The story's ending is heartbreaking, and isn't soon forgotten.

In the episode's last moments, Kirk, Spock, and McCoy (recovered from his condition) return through the portal to find that the Enterprise exists once again, inviting them to beam up. The Guardian of Forever confirms that their mission was a success:

The Guardian in The Animated Series

The Guardian's parting words suggest the potential for future temporal adventures. However, the Guardian only had one more canon appearance before its return in Discovery. In 1973, it was shown in the second episode of Star Trek: The Animated Series, "Yesteryear." As the episode opens, viewers see Starfleet historians and researchers using the portal to study history. Of course, this has consequences. The episode revolves around Spock failing to save the life of his child self, thus erasing his existence in the present. Thankfully, the Guardian is cooperative in helping Kirk and the rest restore the universe to its status quo.

"Yesteryear" seems to suggest that Starfleet had been using the Guardian to observe and catalog history for some time. However, there is no mention of this in any other canon media. A possible in-universe explanation is that the project was scrapped after Spock's debacle, out of concern about creating further disturbances in the timeline.

The Guardian in Star Trek: Discovery

In Season 3 of Star Trek: Discovery, the ship and her crew have jumped 950 years into the future to arrive in the 32nd century. Naturally, it's a big adjustment for everyone, but Phillipa Georgiou has the worst of it. Soon after the jump, she begins experiencing strange, painful physical symptoms. Dr. Kovich explains that since Georgiou has both traveled through time and crossed over from the mirror universe, her body is essentially tearing itself apart. The ship's computer (aided by the mysterious sphere data) suggests that the cure for Georgiou's condition may be found on a planet called Dannos V. Her chances are slim, but Michael Burnham is determined to try. She and Phillipa beam down to the planet, a barren wasteland of snow.

Following the coordinates, Michael and Phillipa stumble upon what Michael describes as "not exactly a life sign." As if from nowhere, a man appears, sitting in a chair. Beside him, standing upright in the snow, is a door. He introduces himself as Carl, and states that the door is here so that Phillipa can go through it.

Running out of time, Phillipa agrees to go through, where she finds herself reliving a pivotal day from her past as the Terran Emperor. Throughout the ensuing two-part story, "Terra Firma," she reexperiences the cutthroat reality of her life in the Mirror Universe. It's an emotional rollercoaster, a reflection on how Phillipa Georgiou has evolved. As Phillipa, following a mutiny, appears to die, she wakes up on the snowy planet with Michael and Carl. Her wristband registers three months of biometric data, but Michael states that less than a minute has passed. It is then that Carl reveals (using archival audio from TOS) his true identity:

The door bursts into pieces, reforming into the familiar shape of the portal from TOS. Carl describes himself as a "space-time portal," and explains that long ago, people used him to travel freely. However, during the Temporal Wars, things changed as factions from across the galaxy tried to use his power to destroy each other. Not wanting to be used as a weapon, he went into hiding.

The Guardian offers to send Phillipa back to a time when the prime and mirror universes were still aligned, preventing her from falling apart at the atomic level. Her journey back to Terra had been a test to see if she would make different choices, given the chance — and she passed. With an emotional goodbye to Michael, Phillipa Georgiou steps through the portal, departing the show for good. As she does, both the gate and Carl vanish.

What Is the Guardian Of Forever?

Interestingly, none of its canon appearances answer that question. In "The City on the Edge of Forever," the Guardian states that it "was made to offer the past in this manner," when Kirk asks if it can speed up or slow down the time at which history passes. To say that it "was made" suggests, of course, that the Guardian was created by someone or something. However, in both TOS and Discovery, it appears on uninhabited planets. Whoever or whatever made the Guardian either abandoned their creation, or is no longer in this universe.

By the 32nd century, though, the Guardian of Forever's powers have grown significantly. It is able to not only send Georgiou back in time, but to another universe. What's more, she returns not as an observer, but in the body of her past self. After 900 years, it's likely that the Guardian learned and evolved, gaining new abilities. His sentience, though, was present right from the beginning.

Considering the 900-year gap between "Yesteryear" and "Terra Firma," it's entirely possible that the Guardian of Forever may make another appearance. Carl himself stated that he was in frequent use up until the 30th century's Temporal Wars. Considering that much of this time is unexplored, there's plenty of room for a future story to answer the questions surrounding the Guardian. Then again, Carl is a cryptic fellow. Perhaps he'll keep his secrets to himself for eternity.

Star Trek: Discovery

Action

Adventure

Drama

Release Date

September 24, 2017

Creator

Bryan Fuller, Alex Kurtzman

Network

CBS

Streaming Service(s)

Paramount+ , Paramount+ with Showtime , fuboTV , Spectrum