The Witch-king of Angmar, also known as the Morgul-Lord, was once a King of Numenor, and later the Lord of the Nazgûl. When Sauron gave him and eight other men Rings of Power, they grew increasingly powerful, but eventually were transformed into wraiths, called the Nazgûl or Ringwraiths. Two thousand years before the Lord of the Rings, he killed the last known king of Gondor, and Glorfindel prophesied that the Witch-King would not fall by the hand of man.
After the Dark Lord was destroyed, Sauron fled Mordor and went into hiding in Dol Guldur, a ruined stronghold that is now abandoned. The Witch King helped him take the form of a dark sorcerer, known as the "Necromancer". When Radagast the Brown, one of the Istari, went to investigate, the Witch-King briefly battled him before being defeated.
On Weathertop, he and four other Ringwraiths confronted the four hobbits: Frodo, Sam, Merry, and Pippin. When Frodo refused to give him the One Ring, he stabbed Frodo with a Morgul blade. He then retreated with the other four Ringwraiths when Aragorn attacked them with his sword and with a burning brand.
Later, when Frodo, Sam, and Gollum passed by Minas Morgul, they saw the gates of Minas Morgul open, and Orcs of Mordor came through, led by the Witch-king. The Witch-king lead an army of Nazgûl, orcs, Easterlings, Haradrim and trolls to take Osgilliath. A few days later, the Morgul Lord led the siege on Minas Tirith and the battle of the Pelennor Fields. While Gandalf the White and Pippin were on their way to save Faramir son of Denethor, the Witch-king stooped down, stopping them. When Gandalf told him to leave, the Witch-king pulled out his sword, and Gandalf's staff broke. During the Battle of the Pelennor Fields, he killed King Théoden, but was then confronted and killed by Merry and Éowyn, causing him to die not by a hand of man but by a woman and a hobbit.