Portal

From Memory Alpha, the free Star Trek reference.

The Portals were guardians of the Tkon Empire that confronted all those seeking entry to the Empire and decided which petitions for entry would be granted. Portals were invested with tremendous power, including the ability to immobilize starships and manifest themselves in various corporeal forms according to the appearance of the petitioners. The Portals also had some form of telepathy. (TNG: "The Last Outpost")

See: Portal 63