Herku is a city in the Winkie Country with a strange master/slave society.
Herku is built to a square plan, surrounded by four walls, each with a burnished copper gate in its center. It is isolated, and visitors from the rest of Oz are almost unknown.
Once each year, the residents of Herku take a teaspoon-sized dose of zosozo, a specially-compounded substance that is a form of pure energy. Zosozo makes the residents skeletally thin but immensely strong — so strong that they have no trouble controlling the breed of giants that they keep as slaves. The giants are twenty feet tall, are armed with tree-trunk-sized clubs, and wear golden collars around their necks as badges of their servitude. (The Lost Princess of Oz)
Herku is ruled by a Czarover named Vig. He has his hands full controlling his difficult subjects; but since he compounds the zosozo himself and controls the secret of its making, his power is generally secure.