Hermethican

The Hermethicans were a species native to the planet Hermethica. A group of criminals lead by the Wire discovered how to convert themselves into pure energy. (PROSE: The Time Travellers' Almanac) The Wire was sentenced to death by her people and eventually executed. However, she became a being of pure energy, and escaped via a mobile communications device, and fled across the universe to Earth in 1953 where she became trapped in a television set. (TV: The Idiot's Lantern)

Behind the scenes
The true form of the Wire or her species, beyond the fact that they were not naturally formless, is unknown, since she was using the image of a BBC continuity announcer that was on the television when she possessed it.