Gorbag the captain of the Uruks of Minas Morgul. He served the Nazgûl who dwelt in the Dead City but he found them disturbing so he moved to Cirith Ungol with Shagrat.
During the War of the Ring it was Gorbag and Shagrat who came across Frodo Baggins who was paralysed by Shelob. They took Frodo back to Cirith Ungol where they would strip him of his posessions.
It was then that a fight brooke out over who would get to keep the Mithril vest, during the fight Gorbag was slain by Shagrat.
In Peter Jackson's The Return of the King Gorbag is portrayed as a smaller Orc while Shagrat is a Uruk. It also shows Samwsie Gamgee killing Gorbag rather than Shagrat.
In The Return of the King video game Gorbag appears as a boss at the end of the "Cirith Ungol" level. In the game, Gorbag knocks down Shagrat and then Sam must defeat him by stunning him with pikes.