Dunlendings, also known as Wildmen of Dunland, were the people of Dunland. They were known as a fierce culture of Men who sought vengeance on the people of Rohan who, as Saruman rightly said, drove them into the mountains. 

 

Saruman uses their anger as a manipulation and convinces them to destroy the land of Rohan during the War of the Ring. He sends them across Rohan, burning and looting the land.