Coldhands

From A Wiki of Ice and Fire

Coldhands is the mysterious figure who saved Samwell Tarly, Gilly and her son when they were beset by wights and lost north of the Wall. Though he could not pass through it himself, he lead them to the Black Gate which passed underneath the Wall into the well of the Night Fort's kitchens.

His hands are black and as cold as ice, and he rides an elk. A flock of ravens flies under his command.