In the fiction of J. R. R. Tolkien, the Witch-king is the chief of the Ringwraiths of Middle-earth.

The Witch-king was originally a human king. In the Second Age, he was given one of nine Rings of Power to help rule over his realm. He and eight others were ensnared by Sauron, who made them the Nazgûl. He became the lord of the Wraiths, and Sauron's chief Servant. It was said that no man could slay him. He later founded the realm of Angmar, and then besieged and took Minas Ithil, renamed it Minas Morgul, and became its lord. Eärnur, King of Gondor, who had previously defeated the Witch-king at the Battle of Fornost but not slain him, foolishly accepted his challenge to meet him in single combat in Minas Morgul, and never returned. From that day until the coronation of Elessar Gondor was ruled by a Steward.

He led the search for the One Ring, and later Mordor's assault on Minas Tirith. Here he slew Theoden of Rohan, but was slain by Theoden's niece Éowyn with the aid of the Hobbit Meriadoc Brandybuck, thereby fulfilling the geas that no man should slay him.