Earth ape which lived — unbeknownst to most humans — under the Antarctic ice cap. Aliens trying to take over Earth accidentally released the Ice Apes. Trying to demonstrate their power to the human governments, the aliens detonated a small explosion on what they thought was the lifeless ice of the Antarctic. Instead, the explosion revealed the home of the Ice Apes and brought the TARDIS down to land on the ice cap.
The Second Doctor and Jamie McCrimmon had to deal with both the angry apes and the power-hungry aliens. In the end, the apes' superior strength allowed them to overcome the aliens, and the two threats cancelled each other out.