Guardian of Forever

The "Guardian" is a nexus of temporal and transdimensional energies created in the appearance of a great archway.

Prime Universe

 * ''See Guardian of Forever at Memory Alpha.

Mirror Universe
It is believed that a mirror version of the "Guardian of Forever" existed in the mirror universe. No concrete evidence has been proven since it was destroyed shortly after 2267 by the Terran Empire.

Warship VOY
In a parallel universe, an entity known as the "Guardian of the Future" existed as part of an inter-quadrant gateway between the location of the actual "Guardian" in the Delta Quadrant of the parallel universe and the portal to that planet, located on a moon of Cardassia in the prime universe.

In 2405, Young and K'hallA, who acted as captain of the USS Enterprise (NCC-1701-C) while her husband suffered under the affliction of the rage virus, were recruited by Katherine Ann Janeway and Benjamin Sisko