The Others

From Asoiaf

The Others make no sound. They come with a sudden cold. They are tall, gaunt and hard as old bones, with pale flesh and deep blue eyes. The Others are clad in armor that changes color as they move and wield longswords made of translucent crystal, a fain blue shimmering on the edges. Those they slay come back to life as wights.

According to Old Nan wilding women lay with the Others in the Long Night to sire terrible half-human children.

The Others killed Ser Waymar Royce of the Night's Watch when he was searching an abandoned wilding camp. When Waymar came back to life he killed his fellow Brother Will.