Prisoner Zero

Prisoner Zero was a shape shifter and a prisoner of the Atraxi.

History
Prisoner Zero was a captive of an Atraxi extra-dimensional prison who escaped through a crack in the universe to Amelia Pond's house on Earth. Prisoner Zero hid within a room in Amelia's house, placing a Perception filter on the door to the room so that it would never be found. There it hid for twelve years, sometimes venturing out into the village, posing as people who it had established a psychic link with (a process that took months). This rendered them comatose. Prisoner Zero drew its forms from their subconscious, and would incorporate other people or animals they imagined being with them, making it appear to be multiple beings touching each other when it was in fact one multi-headed creature. Rory Williams, who worked at the local hospital as a nurse, often saw Prisoner Zero in its various forms and took pictures of them with his BlackBerry Storm, knowing that the people he saw shouldn't be up and about. Later, this was the favourite part of the Doctor's plan to bring Prisoner Zero into the open. It was during this time that Prisoner Zero established a Psychic link with Amelia (later Amy) Pond. The Doctor belatedly returned to Amelia's house, followed by the Atraxi, who broadcast a global warning that they would incinerate "the human residence" (Earth) if Prisoner Zero did not surrender. Prisoner Zero fled. The Doctor and Amy went into the village square, where residents of Leadworth were taking pictures of the Sun, obscured because the Atraxi had put a force field around the Earth. The Doctor noticed that Rory was facing the other way, taking a picture of Prisoner Zero, which was disguised as a man with a dog. The Doctor attempted to draw the Atraxi to Prisoner Zero by overloading all the electrical devices in the surrounding area with his extraterrestrial sonic screwdriver. The attempt failed, and Prisoner Zero melted away.

Prisoner Zero arrived at the hospital and proceeded to kill all the doctors and nurses, including Doctor Ramsden. Prisoner Zero then took the form of a woman with two children, and was found by Amy and Rory. Prisoner Zero gave itself away by talking with the woman's voice through a child's mouth. It snarled at Amy and Rory and chased them down the corridoors. The Doctor arrived through the window just in time, and revealed his master plan to Prisoner Zero.

Then the creature revealed a ominous prescience, identifying the Doctor as a Time Lord and taunting him that "The universe is cracked. The Pandorica will open. Silence will fall". Believing that surrender would mean execution, Prisoner Zero said it was prepared to die in flames with the whole planet. When cornered by the Doctor, it tried to avoid Atraxi detection by making a psychic connection with Amy and using her memories to imitate her younger self and the Doctor.

The Doctor thwarted this by stimulating Amy's recent memory of Prisoner Zero and forcing it to take on its own form. The Atraxi detected and secured Prisoner Zero, as it gave its final warning: "Silence, Doctor. Silence will fall" (DW: The Eleventh Hour).

It is advanced enough to know that the Doctor is a Time Lord, which most species are unable to recognise. It did not create the crack through which it escaped, but was aware of what caused it - knowledge that it discovered the Doctor did not possess.

Behind the scenes
In an issue of Doctor Who Magazine, Matt Smith and Karen Gillan refered to Prisoner Zero as a "Face Tendril".