Rock Troll

Rock, stone, the very earth itself give these creatures their strength. Ugly and fat looking, they are often grey skinned. Strong as the stone they come from, they are difficult to hurt; their skin is tough and can damage the edge on sword and axe. Spears may have a tough time penetrating.
They are arrogant, because they are aware of how strong and tough they are. And they tend to be rather stupid. It is this that makes them vulnerable, for they may be fooled into doing things that a more intelligent being would not. Stories abound of those who have fooled them into killing themselves in various ways, from self immolation to poison to jumping off cliffs.
Rock trolls start out small and grow throughout their lives, getting to be as large as some of the largest giants, if they live that long.