The Autons are plastic mannequins that are controlled by the Nestene Conciousness. When the Nestene first tried to invade Earth the Autons were created in a plastics factory that created shop mannequins as well as displays for Madame Tussauds.
The Autons were discovered when UNIT began to investigate the plastics factory after a former employee, after being fired, broke into the factory and was pursued by an Auton.
The Autons have a deadly weapon located in the right hand. The fingers are on a hinge, and drop out of the way to reveal the weapon. The first shot kills, and a second shot can be used to disintegrate the target.
Autons are practically indestructible, being made entirely of plastic. Although bullets do cause damage, the Third Doctor managed to create a device that could jam the frequency used by the Nestene Conciousness. Once this control link was severed the Auton reverted to being an inert plastic mannequin.
The ninth Doctor could also break the control using his sonic screwdriver, but this meant being very close to the target.