Hider

A hider was the name used by the Church of the Outsiders for aliens who lived amongst humans in secret. Erin Lewis surmised that Ianto Jones had likely spent a lot of time around them. (AUDIO: Believe)

The Zygons became hiders as a result of Operation Double. (TV: The Day of the Doctor, The Zygon Invasion/The Zygon Inversion)