The Others (known in the show as the White Walkers) are an ancient race of humanoid ice creatures that are vaguely thought to have originated from the Lands of Always Winter. Certainly not human in nature, the Others are simply humanoid in appearance. They are taller than the average human, with glowing, icy blue eyes, wispy white hair (at least on most of them) and pale, grey-white skin, looking almost mummified. In the books, they also wear a sort of delicate, reflective, camouflaging armor that shifts in color with every step. In both, they wield crystal swords and spears capable of shattering conventional weaponry with its icy touch: just the mere touch of a weapon from an Other will result in it shattering. As such, conventional weapons cannot kill an Other, although dragonglass, as well as Valyrian steel, can kill them, as well as deflect their weapons.
The Others are few, although it's possible they were greater in number during the Long Night, before they were thought to have been hunted to extinction. However, the Others, possibly through necromancy, are capable of raising the dead of the slain, turning them into undead servants of their army: they can do this to any sentient creature, even giants.