The king of Nupe is called the Etsu Nupe. "Etsu" means "ruler" in the Nupe language, and the Etsu Nupe is the traditional leader of the Nupe people, who are predominantly found in Nigeria's Niger State. The Etsu Nupe is responsible for maintaining the customs and traditions of the Nupe people, as well as serving as a spiritual and cultural leader. The Etsu Nupe is also involved in governance and decision-making, particularly in matters concerning the Nupe kingdom. Therefore, out of the options given, the correct answer is "Etsu Nupe."