A hood is a cloth covering of the head and neck, with an opening for the face. Recently, hoods are back in fashion, though renamed -- at least informally -- hoodies.
Consider the fearsome Law Givers of planet Beta III in Star Trek's (1966 - 1969) "Return of the Archons" in 1967. We never see the faces of these individuals, as their visages are cloaked beneath hoods.
In the animated series, Return to the Planet of the Apes (1975), the subterranean denizens of the Forbidden Zone -- known as the Underdwellers -- similarly wear cloaks to hide their faces.
In Space: 1999 (1975 - 1977) one episode, "Another Time, Another Place," features a creepy dream in which an Alphan, Regina (Judy Geeson) is facdd with a grim-reaper-like doppelganger. That doppelganger's pale face is draped in a black hood.
In Star Trek: the Next Generation (1987 - 1994), the Portal of the T'Kon Empire also wears a hood while testing the relative values of the Enterprise crew and the Ferengi.
More recently, heroes have taken to wearing hoods. Michonne (Danai Gurira) -- the ultimate survivor on AMC's The Walking Dead (2010 - ) is first introduced brandishing a katana and protecting her face underneath a hood. She is a fearsome enemy, indeed.
Similarly, both Smallville (2011 - 2011) and Arrow (2011 - ) have re-imagined the DC hero Green Arrow and his costume. He no longer wears a Robin Hood cap, but instead dons a hoodie.