The Guardians are among the most mysterious of the many entities the Doctor and his companions have come up against. Sometimes known as the Guardians of the Universe or the Guardians of Time and Space, they werent the first omnipotent beings to appear in Doctor Who. However, the Doctor has come into contact with these powerful entities more than any other. Their introduction during a season-long arc in the mid-1970s was enough to earn them a returning trilogy during the shows 20th anniversary season.