Appearing in the first episode featuring Matt Smiths 11th Doctor, The Eleventh Hour, Prisoner Zero is a scary piece of work in an episode (written by brand new showrunner Steven Moffat) thats pretty determined to creep the viewer out as much as possible.An escaped alien convict (or, as the Doctor puts it, an interdimensional multi-form from outer space) on the run from a race knows as the Atraxi that, in its natural form, appears to be a giant, flying alien viperfish, Prisoner Zero doesnt get a proper name, and its race is never formally identified. Telepathic and capable of creating a powerful perception filter in a similar way to the TARDIS, Prisoner Zero hid in Amy Ponds house for twelve years, taking on the forms of comatose patients in the nearby hospital. But its that scene with the fanged maw hiding behind Amy that people remember the most and the insinuation that this isnt the whole creature, but rather, a limb - or one of many, many heads