Who leads Sauron's army in the battle against the city of Minas Tirith?

The Witch-king of Angmar leads Sauron’s army against Minas Tirith during the Battle of the Pelennor Fields. He is the Lord of the Nazgûl and Sauron’s chief lieutenant, making him the principal commander of the assault from Mordor.

Before the main battle, the Witch-king uses the battering ram Grond to break Minas Tirith’s great gate. He then commands the besieging forces as the Rohirrim arrive to aid Gondor. His presence is meant to terrify the city’s defenders as much as to direct the military attack.

The Witch-king is not Sauron himself: he was once a mortal king of Men corrupted by one of the Rings of Power. He is ultimately defeated by Éowyn, disguised as the warrior Dernhelm, with help from the hobbit Merry. Azog belongs to The Hobbit, while Saruman commands forces from Isengard.