There are "The Others" or "White Walkers" as the Wildlings call them. They are a whole other race that haven't been seen for thousands of years, but popped up recently.
In the books, they look more like normal humans, but tall and slender with pure white skin and pale blue eyes.
In the TV series they look more like 'creatures'
They create "Wights" which are the zombies. They use humanoid wights as armies, and animals to ride.
So "The Others" which are known as "White Walkers" in the TV series, look like "White Walkers" and "Whights" could look like zombified versions of anything - even animals.