The Witch-king of Angmar was originally a great Númenórean king. In the Second Age, he received Ûri (Heart-stopper), one of the nine Rings of Power given to Men by the Dark Lord of Mordor, Sauron. The Rings gave them incredible power, which they used to further their own ambitions, but eventually the Rings completely corrupted them and turned them into the ghastly Nazgûl.
He founded the kingdom of Angmar. It was after the formation of Angmar, and several conflicts with the Dúnedain of the North, that the Lord of the Nazgûl became widely known as the Witch-king, Lord of Angmar, reflecting the fact that he practiced black sorcery. Because of the great havoc he wrought in the north, he became notorious among the peoples of Middle-earth as the terrible Lord of Angmar; thus, he thereafter retained his title of Witch-king, even long after he left Angmar.
In the game's introductory cutscene he is seen standing at the Witch King's Watch calling forth an army "from the depths of Carn Dûm".
The Witch-king leads the other eight Nazgûl against the guard of Rangers at Sarn Ford the evening of September 22, 3018, forcing their way across the Brandywine and into the Shire.
Some other characters encounter the Witch-king for the first time in the Great Barrow, where he is giving orders to Skorgrím Dourhand and Ivar the Blood-hand. He cannot be fought, but his scream inflicts +9 Dread and causes players to cower in fear.