Alaafin, or The custodian of the Palace in the Yoruba language, is the title of the king of the medieval Oyo empire and present-day Oyo town of West Africa. It is the particular title of the Oba (king) of the Oyo. It is sometimes translated as "emperor" in the context of ruler of empire. He ruled the old Oyo Empire, which extended from the present-day Benin republic to Nigeria, originating from states in the South East and West to the North. The people under him are called Yoruba people and spoke the Yoruba Language.

The Oyo Empire was a Yoruba empire in West Africa. It was located in present-day southern Benin and western Nigeria. The empire grew to become the largest Yoruba-speaking state through the organizational and administrative efforts of the Yoruba people, trade, as well as the military use of cavalry. The Oyo Empire was one of the most politically important states in Western Africa from the mid-17th to the late 18th century and held sway not only over most of the other kingdoms in Yorubaland, but also over nearby African states, notably the Fon Kingdom of Dahomey in the modern Republic of Benin on its west.