Wormtongue:

Servant of Théoden and later a spy for Saruman, Wormtongue did much evil in the land of Rohan. When he had been discovered, Wormtongue was given a choice: to either go with King Théoden into battle, or to go where he would. He chose the latter, and was later imprisoned in Orthanc with Saruman. Wormtongue was later killed by hobbit archers after murduring Saruman in the Shire.

The Witch-King:

One of the nine Nazgul or Ringwraiths, the Witch-King was once a Man. He was given one of the Nine by Sauron. He was also known as the Lord of the Nazgul. As the ruler of the realm of Angmar, the foe of Arnor, he gained the name 'Witch-King'.

This was the Nazgul who wounded Frodo on Weathertop. Other events in which he participated included the Battle of the Pelennor Fields where he was killed. Frodo watched him lead an army out of Minas Morgul in preparation for this. Prior to the War of the Ring, the Lord of the Nazgul was the one who ended the line of the Kings of Gondor with Earnur. He was also a leader in the search for the One Ring.

The Battle of the Pelennor Fields was his last, for after causing the death of Theoden, the King of Rohan, he was killed by the combined effort of Eowyn and Meriadoc Brandybuck.

When the forces of Angmar were defeated, Glorfindel foretold of the Witchking that "not by the hand of man will he fall" (LOTR.1088). This proved true at the Battle of the Pelennor Fields.

The Lord of the Rings
The Silmarillion
The Hobbit
The Complete Guide to Middle Earth by Robert Foster