Corrupted treant

From WoWWiki

Corrupted treants are wretched tree-creatures who were once proud, immortal defenders of Ashenvale forest. Yet, when the Burning Legion invaded the world in ages past, its demonic energies corrupted many of the ancient tree-men and drove them into shadow. Now these tortured creatures live only to spread their corruption and hatred of all living things.^{W3Man 141}

In World of Warcraft

They appear as Withered Ancients in northern Ashenvale.