In The Lord of the Rings
During the War of the Ring, Sauron and his ally Saruman sent a band of Uruk-hai, Mordor Orcs and Moria Orcs to capture two hobbits of the Fellowship. They were at one time led by Grishnákh, a captain tasked with taking the hobbits back to Mordor. These orcs managed to kill the warrior Boromir and to capture Merry and Pippin, whom they had mistaken for Frodo and Sam. However, as they left Amon Hen they began to quarrel over where to take them. The Mordor Orcs had received orders to take them to their master Sauron while the Uruk-hai were to deliver them to Saruman in Isengard. Since the orcs of Isengard were more numerous than those of Mordor, Grishnákh's band was forced to follow the Uruks. The orc captain secretly planned his next move and left the group to call reinforcements. At night near Fangorn Forest, however, the orcs were all killed by the Riders of Rohan.
Thousands of orcs were led by the Witch-king against the forces of Gondor at the battle near Pelennor Fields, after their defeat of the defenders of Osgiliath, and their siege of Minas Tirith. The rest of the Mordor Orcs perished at the Battle of the Black Gate, or in the destruction of the Dark Tower.