Gorbag was the captain of the orcs of the Red Eye
symbol for Sauron on their livery), which Shagrat called the
In the tower of Cirith Ungol, Gorbag tried to take Frodo's mithril shirt. Shagrat, captain of the tower, fought with him over it, as all items on the halfling needed to go to Lugburz or Shagrat could expect to go to the Black Pits. He may well have had some idea of keeping it too. Gorbag had warned Shagrat of the enemy warrior still loose that they needed to handle, but Shagrat did not consider a problem.
Gorbag knifed Shagrat who throttled him, but later the apparently dead Gorbag struck at Shagrat with a broken spear, perhaps accidentally saving Snaga whom Shagrat was chasing, as Shagrat had to stop to knife him.
Reference: Return of the King: "The Tower of Cirith Ungol"
Dec. 3, 2002
Gorbag was a sergeant of the Orcs in Minas
Morgul, charged with patrolling
the Stairs leading to the Tower of Cirith Ungol. He was slain in
by Shagrat in a dispute over Frodo's magic items. The quarrel
Orcs led to a full scale battle between their troops, and this allowed
to rescue Frodo from the Tower.