Guardian of Forever
The Guardian of Forever is a mysterious construct of an unknown, ancient alien race.
It functions as a time portal, a gateway to the time vortex that allows access to other times, locations and dimensions.
Located on an ancient planet in the Beta Quadrant, its location is the focus of all timelines throughout (at least) the Milky Way Galaxy converge.
Positioned among the eventual ruins of a large, forgotten city, the ruins appear to be at least one million years old.
The Guardian of the time vortex has been documented as stating that it was far older than that estimated age, even exceeding the Earth's sun's age of 4.6 billion years.
The "Guardian of Forever," as it calls itself, appears as an inert, circular gateway, comprised of a quasi-metallic substance.
It is able to display the flow of time itself, although it can not alter the speed at which it displayed the past.
Generating immense ripples in time, these manifest themselves as spatial disturbances in the region around the planet where it is located.
A sentient being of some form, it is capable of speech, and interacts with anyone it encounters.
The gateway itself flashes whenever it spoke, and emits a gaseous fog within its center whenever it generated a portal.
The Guardian has been said to speak "dispassionately" and logically. It appears to be ambivalent to changes in the timestream, neither being able to prevent individuals from going back in time using it, or interfering with those who attempted to use it to set the timeline right. It has been willing to assist when asked, such as agreeing to replay its images of Earth history in order to allow Spock to more precisely estimate when Leonard McCoy arrived in Earth's past, causing a timeline schism.
As far as Federation history is concerned, the Guardian was first discovered by the crew of the USS Enterprise in 2267. When they encountered powerful wave of space displacement, they traced it back to a planet whose location is now listed as "HIGHLY CLASSIFIED." The crew encountered and made contact with the Guardian, who offered them the chance to explore the past. Suffering from temporary mental psychosis, Dr. McCoy jumped through the portal at a random time, arriving in 1930. His actions in this year accidently caused the aggressor of WWII to win the war, contrary to the current timeline. The Enterprise's landing party lost contact with the ship, as the ripple effect caused history as they knew it to drastically change.
In order to restore their timeline, and the presence of their ship in orbit, the rest of the away team followed McCoy through the portal, with the Guardian allowing them to jump to a point before McCoy's arrival. Having to do this a number of times in order to pinpoint the exact moment history changed, as well as rescue their fellow crewmember, the away team realized that the prevention of one civilian's death had affected them all.
Two years later, a team of Federation historians used the Guardian's abilities to investigate Federation history. They were able to view first-hand accounts of the Orion civilization's formation, as well as Vulcan history from the 2230s to the 2240s.
