(covers information from several alternate timelines)
- "Are you machine, or being?"
- "I am both... and neither. I am my own beginning, my own ending."
The Guardian of Forever is a construct of an unknown, ancient alien race, that functions as a time portal, a gateway to the time vortex that allows access to other times and dimensions. It is located on an ancient planet where the focus of all timelines throughout at least the Milky Way Galaxy converge. It is apparently sentient, responding to external stimulus such as questions and actions, and can even somehow control the flow of time. It generates immense ripples in time that manifest themselves as spatial disturbances in the region around the planet where it is located.
The Guardian is located among the ruins of a large, forgotten city that stretched beyond the horizon in all directions around it. Based on initial observations, the ruins appeared to be at least one million years old.
Capable of speaking to those around it, the Guardian explained that it is "its own beginning and its own ending," and that, "since before your sun (Sol) burned hot in space, [it had] awaited a question." Apparently an inert formation of quasi-metallic substance, the Guardian creates portals to other times.
The Guardian was first discovered by the crew of the USS Enterprise in 2267. Encountering powerful waves of space displacement, which Spock described as "ripples in time," the Enterprise tracked the waves back to their point of origin on a previously-uncharted planet. Doctor McCoy, suffering from paranoid delusions as a result of an accidental overdose of cordrazine, beamed down to the surface in an attempt to escape the ship. Searching for McCoy, Captain Kirk and Spock encountered and made contact with the Guardian, who offered them the chance to explore the past. As the Guardian was displaying images from Earth history, McCoy emerged from hiding and leapt through the time portal, arriving on Earth in the year 1930. The landing party soon discovered that they had lost all contact with the Enterprise, and the Guardian informed them that McCoy had effected a change in history, wiping out their civilization. Realizing that they must correct the damage to history, Kirk and Spock had the Guardian replay Earth history, and traveled through the portal to a point in time prior to McCoy's arrival. Eventually successful in their effort to restore the timeline, the Guardian returned all three of them to their proper place and time, mere moments after they initially departed. (TOS: "The City on the Edge of Forever")
In 2269, a team of historians, accompanied by Captain Kirk and Spock, used the Guardian to investigate Federation history. Their investigation included firsthand accounts of the formation of the Orion civilization and the monitoring of Vulcan history of the 2230s and 2240s. While Kirk and Spock were visiting Orion, their support team was monitoring Vulcan's past, which, in doing so, inadvertently removed Spock from the proper timeline. Spock, however, was protected from the change while he was in Orion's past, and the change to the timeline went unnoticed until he and Kirk returned through the Guardian. Once the cause was determined, Spock was able to use the Guardian to return to his own childhood on Vulcan, and prevent his death during the kahs-wan ritual. (TAS: "Yesteryear")
Images seen through the Guardian of Forever
In the original teleplay for "The City on the Edge of Forever," the Guardians of the Time Vortex were nine feet tall, humanoid statue-like beings.
An original draft of the episode that eventually became TNG: "Yesterday's Enterprise" featured a Vulcan science team researching history through the Guardian of Forever. In that story, the team accidentally caused the death of Surak, the father of modern Vulcan philosophy - as a result, the Time of Awakening never occurred, and the Vulcan race had essentially evolved as the Romulans. The time line would be reset when Sarek, aboard the Enterprise-D to greet the scientists, would use the Guardian to go back in time and take Surak's place in history. (Star Trek: The Next Generation Companion)
The original Guardian was designed by Desilu Supervising Art Director Rolland M. Brooks, because Matt Jefferies was sick with the Flu that week. (Star Trek: The Animated Series DVDs, text commentary for "Yesteryear")
The Guardian's last words in City on the Edge of Forever were "Many such journeys are possible. Let me be your gateway". This suggested that further stories could be written involving the Guardian. However, although the Guardian appears in many apocryphal stories, its only other on-screen canonical role was in the animated episode Yesteryear.
The Guardian appears in the game Star Trek Online in a mission involving the players character breaking the quarantine of the guardian's planet. The player must travel through the portal in order to follow a group of Klingons and stop them from destroying the Enterprise from the Original series and rescue Miral Paris. This is one of the few appearances of voice-overs in the game.
In the novel Yesterday's Son, Kirk and Spock use the Guardian to rescue Spock's son Zar from the ancient, doomed world of Sarpeidon. They also discover that Zar is able to communicate telepathically with the Guardian. In the novel's sequel Time for Yesterday, the Guardian is summoned away from its duties of regulating time in the Milky Way by its capricious Creators. Zar uses his telepathic powers to return the consciousness of the Guardian to the gateway and banish the Creators to a universe where they cannot harm our space-time.
In the novel Engines of Destiny, the Guardian appears in an alternate timeline where the Borg have conquered Earth and an alternate Guinan, having learned of the change, has gone to the Guardian's planet to ask for help, and the Guardian reveals how to restore the timeline to normal.
In the novel The Devil's Heart, the titular object, an ancient stone rumored to have vast powers, is revealed to be a "seed" created by the same civilization who created the Guardian, and meant to create another Guardian on the world it was sent to, before it went astray.
In the novel First Frontier, members of the Clan Ru, a species whose pre-sentient ancestors - Earth dinosaurs - had been rescued by the Preservers before the mass extinction, used the Guardian to destroy the asteroid which would hit Earth, allowing their species to remain and evolve there. The timeline would be reset by Kirk, with the assent of the Clan Ru, when they discovered that in this altered history, their species destroyed itself in a series of nuclear wars before it could reach the stars.
In the Q Continuum series, the Guardian is used by a younger Q when attempting to find something new, allowing him to make contact with the being known as 0 (although the Guardian briefly tries to deny 0 access to this universe), who subsequently contacts (*), Gorgan and The One via the Guardian. It is hinted here that the Guardian was built by the race that would eventually evolve into the Q – when looking at the Guardian, the young Q comments "At least our ancestors made things", reflecting his dejection at the stagnant nature of the Q Continuum – but the veracity of this is uncertain, and given the nature of the Guardian, Q's comments might have been influenced by images he perceived within it.
In the alternate future seen in the Star Trek: Deep Space Nine book trilogy Millennium the Guardian of Forever was key to Admiral Kathryn Janeway's Project Forever. Janeway, along with a combined Federation/Borg armada hoped to use the Guardian to go back in time and wipe out Bajor (the Federation was at war with the Bajoran Ascendancy in this timeline and were facing the end of the universe). However, at the very moment that Janeway and a team arrived at the Guardian, the Grigari set off a singularity bomb, creating a black hole that destroyed the entire Federation/Borg fleet, the Grigari fleet, Janeway, and the Guardian. The timeline was later reset by Benjamin Sisko and the crew of Deep Space 9.
In the alternate future presented in Imzadi, Admiral Riker used the Guardian to travel back in time to save Deanna Troi's life from an attempt to kill her and prevent her participation in a conference. In the timeline where she died, the species involved went on to secretly rebuild and become a major military power, but with her survival, Troi's empathic powers revealed that they were lying to gain time, and the conference was abandoned until the species was in desperate need of assistance. Although the future Data also attempts to travel back in time to maintain continuity (Riker is convinced to travel back after new evidence suggests that Troi was killed by a time-traveler, but Data feels that Riker is clutching at straws), it is revealed at the conclusion of the novel that history had already been changed, and Riker's actions actually set it back on the right path.
In Spock Vs. Q, Spock mentions having used the Guardian to travel back to the 20th century. Q describes it as "that lop-sided donut thing" before Spock corrects him, and asks him if he knows it. Q responds "been there, done that, got the T-shirt."
In the novel Provenance of Shadows, the Enterprise returns to the Guardian for a third time, just before the end of its original 5-year mission. They respond to a distress call from the science station erected in orbit of the Guardian's planet. Three Klingon ships attack the station and the Enterprise. They are successful in boarding the Enterprise's bridge and manage to take over the ship, forcing the crew to abandon ship, but Captain Kirk manages to escape, obtain several phasers, and transport down to the planet. There, he steps through the Guardian and ends up back on the Enterprise's bridge moments before the Klingons boarded. As the crew evacuates the bridge, Kirk sets the phasers on overload, and sacrifices himself to kill the Klingons, but his now-alternate timeline counterpart survives. As a last resort, the Klingons crash their ship into the Guardian, apparently destroying it.
In the short story "Guardians" (from the anthology Strange_New_Worlds_VII), the Horta are assigned by the Federation to serve as the protectors of the Guardian after a failed attack/attempt to alter the timeline by the Romulans. Since their lifespan extends for the next 40,000 years, they are witnesses to vast changes in the Federation, the ascendancy of humanity to incorporeal beings and the eventual exploration of the known universe and beyond. The Guardian undergoes periodic attacks and attempted usage from the Borg, the Romulans and the Crystalline Entity, each time defeated by the Horta.