In The Return of the King:
Gothmog commands the successful attack and capture of Osgiliath. He personally finishes off Madril, who was Faramir's lieutenant.
Gothmog then leads the ground forces at the Battle of Pelennor Fields after receiving his orders from the Witch-King, Lord of the Nazgûl. He rides out to the battlefield on a Warg. All goes well for his battle plan until King Théoden and the Rohirrim arrive. He is likely killed in the first charge of the mounted Rohirrim against his orc army. When Aragorn arrives with the King of the Dead, the last of Gothmog's Orcs are annihilated.
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