The Wire
The Wire is an alien life form that was executed by its people but managed to preserve itself as an energy being that escaped to Earth.
It concealed itself in television signals, transferring itself from set to set. It fed to off the mental signals of Humans, paralysing them and then leeching out their energy with electrical tendrils (DW: The Idiot's Lantern) This process would leave the victim mindless, as well as faceless. The Wire used the image of a female BBC continuity announcer to communicate with the outside world. It hoped to use this energy to manifest itself in a corporeal form once more.
The Wire stole the face of Mr. Magpie, who owned an electrical shop, and gave it back to him, giving him plans for then-future technologies (such as televisions small enough to carry in one hand) and promising freedom to him after the completion of its simple two-phase plan: First, have Magpie sell cheap television sets all over North London so it could feed.
Second, have Magpie connect the Wire (inside a portable television) to the television transmission tower at Alexandria Palace on Queen Elizabeth II's coronation day, which would happen June 2, 1953. Connected the tower, the Wire could both transmit itself to the estimated three million viewers watching in the vicinity and transmit back the energy it thought it could use to re-constitute its body.
However, the Doctor was able to trap the Wire on a Betamax tape using a makeshift video recorder. The Wire's victims were then restored to normality. The Doctor seemed confident that the Wire would remain trapped, but said that he would tape over it, just to be safe. (DW: The Idiot's Lantern)
