What is the name of the creature who leads the armies of the main villain in the Lord of the Rings universe?

In J.R.R. Tolkien's Lord of the Rings universe, the creature who leads the armies of the main villain Sauron is called the Nazgûl, also known as the Ringwraiths. They were once kings of Men who were corrupted by Sauron through the nine Rings of Power, which he gave to them. As the Nazgûl, they are bound to serve Sauron and are his most powerful servants. They are invisible to most people, except for those who possess the One Ring, which they seek to retrieve for their master.

The Nazgûl are fearsome opponents in battle, with a number of supernatural abilities such as the ability to instill terror in their enemies, as well as heightened senses and physical strength. They ride on winged beasts called Fellbeasts, which are also under Sauron's control.