Which Tolkien character is known as the Lord of the Nazgûl?

The Witch-king of Angmar is the Tolkien character known as the Lord of the Nazgûl.

The Witch-king is the chief of the nine Ringwraiths, servants of Sauron who were once mortal kings. His personal name is never given in Tolkien’s published narratives. He is identified by titles, most prominently the Lord of the Nazgûl and the Witch-king of Angmar.

In the Third Age, he established the realm of Angmar and waged war against the northern kingdom of Arnor. Much later, he led the assault on Minas Tirith during the War of the Ring. He was ultimately defeated by Éowyn and Merry, fulfilling the prophecy that no living man would kill him.

Khamûl is another named Ringwraith, but he is not their leader. Gothmog is a separate title associated with a lieutenant of Morgul in The Lord of the Rings and with another figure in Tolkien’s earlier mythology.