A mask was an object that completely covered someone's face, frequently to conceal identity.
Uses
The Units wore masks that connected them as a group mind. Akimus Makassar's mask worked as a processing centre, which meant that he could control the will of anyone in the group mind. (PROSE: The Masks of Makassar)
The Aztec High Priest Yetaxa was buried with a mask, while Aztec warriors such as Ixta wore masks as part of their uniforms. (TV: The Aztecs)
Omega wore a mask as he resided in the anti-matter universe. He noted that the Second and Third Doctors would need such masks in time if they were to remain in the anti-matter universe. When Omega removed his mask to prepare for his departure, he discovered that the anti-matter universe had completely dissolved his physical body. He could not leave his universe; he existed only because his will insisted that he exist, but his will was all that was left of him. (TV: The Three Doctors)
Magnus Greel, (TV: The Talons of Weng-Chiang) the Decayed Master, (AUDIO: Dust Breeding) and Elizabeth X (TV: The Beast Below) wore masks to hide their appearances.
Scaroth disguised his various fragments in human form behind masks. (TV: City of Death)
Roboforms wore masks as part of their Santa Claus guises. (TV: The Christmas Invasion, The Runaway Bride)
Some Silurian Warriors wore masks. (TV: The Hungry Earth / Cold Blood, A Good Man Goes to War; GAME: The Eternity Clock'; COMIC: Supremecy of the Cybermen)
The Soulless wore masks as a representation of their belief that Miracle Day had robbed humanity of their souls. (TV: Dead of Night)
Voord masks altered the wearers genetic code and turned them into a Voord, provided they were willing to go through with the ritual. The mask became part of the wearer in the process and removing it could lead to disfigurement. (AUDIO: Domain of the Voord)
Señor 105 made masks representing every element on the periodic table. According to some rumours, he gained powers when he wore the masks. (PROSE: Iris Wildthyme y Señor Cientocinco contra Los Monstruos del Fiesta)
Ben Jackson used Tut-Ankh-Amen's mask to frighten off bandits who had come to rob his tomb. (PROSE: The King of Golden Death)
Goat masks were sometimes worn in occult rituals. (TV: A Girl's Best Friend, PROSE: Timewyrm: Exodus, White Darkness)
Other references
Joy believed that a Silent looked the way it did because it wore a Star Trek mask. (TV: The Impossible Astronaut) Similarly, a hospital porter in Cardiff believed a Weevil's face was a convincing mask. (TV: Everything Changes)
Behind the scenes
The BBC Doctor Who website featured several cut-out masks of aliens from the franchise that could be printed.[1] Masks of varying materials were also available as free gifts in Doctor Who Adventures.