White Walkers possess the magical powers related to ice and cold. Their arrival is usually accompanied by blizzards and the dropping of temperatures. They can also freeze anything they touch, as one froze Sam's sword to the point that it shattered.
However, one of their most deadly abilities is to reanimate the dead as their servants, known as
Wights. They are actually capable of reviving
any dead animals as wights, as a few White Walkers have been seen riding undead horses. When revived, their eyes turn an icy blue, similar to the White Walkers' own eyes. Wights can only be killed by fire and serve the Walkers without question, actual White Walkers can only be killed by Dragonglass (what Sam killed the one in S3 with).