Droid 4

Droid 4 was a construction droid at Martian Lunar Park on Phobos, a moon of Mars.

In 2589, Kai Tobias had reprogrammed all of the construction droids used to build Lunar Park to assassinate the guests, disguising them as native creatures he called Phobians. After the Eighth Doctor and Lucie Miller discovered his plot, Kai knocked them unconscious and ordered Droid 4 to throw them into a wormhole.

Droid 4 was eventually destroyed by the Doctor, who used his sonic screwdriver to unscrew components inside the droid, causing one of its limbs to detach and the rest of its systems to shut down. (AUDIO: Phobos)