The Others (ASOIAF)

The Others, known as the "White Walkers" among the wildlings, exist north of the Wall. Before the events in the novel, the Others had supposedly not been seen for many thousand years. So far the Others have appeared in the flesh only twice in the whole saga and their purpose remains unknown at this time

Characteristics
The Others appear in the prologue to AGoT as tall and gaunt with flesh pale as milk and blue eyes, deeper and bluer than human eyes, burning like ice, while the White Walker who married the Night's King is similarly described as having skin as pale as the moon and eyes like blue stars.

They wear reflective armor that shifts in color with every step rather like the stealth armor once said to have been worn by the Children of the Forest. The go lightly on the snow and leave no prints to mark their passage. They appear to be superior swordsmen, wielding thin crystal swords said to be so cold as to shatter any object they touch, including the steel blades favoured by the Night's Watch.

Their language is unknown, although it may be the Old Tongue. When one spoke in the prologue his voice was said to sound like the cracking of ice, but this was probably a figure of speech. The wildlings believe the Others and their Wights can smell life, or rather its warmth.

The old stories reveal uncertainty whether the Others come when it is cold or that it becomes cold when they appear, during snowstorms or mist and melt away when the skies clear. They hide from the light of the sun and emerge at night; although once again some stories claim that their coming brings the night.

There are tales of their riding the corpses of dead animals such as bears, direwolves, mammoths, and horses, The Other that Samwell Tarly slays is riding Mawney’s dead horse. Hoarfrost covers it like a sheen of frozen sweat, and a nest of stiff black entrails drag from its open belly. On its back is a rider as pale as ice. The Others can be accompanied by "ice spiders" as big as hounds.

Melisandre thinks that Others are servants of the Great Other, allegedly an evil god of darkness, cold, and death who wages eternal war against R'hilor.

Weakness
The Others have a few known weaknesses that are recorded in ancient texts. One is obsidian, otherwise called dragonglass or "frozen fire". When Samwell Tarly accidentally stabbed an Other with an obsidian dagger, its flesh and bones melted away leaving only an icy puddle. Ancient texts also record a weakness to "dragonsteel", which several have taken to be Valyrian steel. Mance Rayder expressed belief that magic wards in the Wall prevent the Others from crossing into the Seven Kingdoms.

Wights
Wights are dead men or creatures raised up by the Others, seemingly when touched by the cold that accompanies them.