The Frost Giants were a race of sentients apparently made out of ice, as they could be melted if exposed to fire. They were eight times as large as Ewoks. Their breathe could freeze other beings to death.
A number of them lived in caverns in the Mountain of Doom on the Forest Moon of Endor. They were ruled by a king, who captured Teebo and Wicket. They were terrified of the fire-breathing dragon-birds of Endor. When the two Ewoks helped them kill a dragon-bird that was harassing their mountain, the Giants helped the Ewoks locat a fire plant, a species unique to the mountain.
Behind the scenes
The Frost Giants may be the same species as the Ice Demon, a gigantic being on Endor also apparently made of ice.