Whimsies have large strong bodies, but their heads are no bigger than doorknobs, making them unintelligent. To cover this fact, they wear big heads made of pasteboard decorated with hair made from colored sheep's wool. Their faces are painted in many ridiculous ways, according to the owner's whim.
They are ruled by the Chief of the Whimsies who is chosen because no one else is wiser or more capable.
The Whimsies are evil spirits and cannot be killed. They are known as terrible fighters because they are so strong and muscular and do not have the sense to know when they are defeated.
General Guph enlisted the aid of the Whimsies in the Nome King's attempted conquest of the Land of Oz. The Whimsies agreed when the General promised that the Nome King would use his Magic Belt to make their natural heads as big and fine as the fake heads they wear.
When the Whimsies and their allies invaded the Emerald City, they drank from the Forbidden Fountain and became as innocent as children, after which Princess Ozma sent them back to their homes. (The Emerald City of Oz)