"Couldn't remember all the goblin rebels' names, so I invented a few.... It's all right, they're all called stuff like Bodrod the Bearded and Urg the Unclean; it wasn't hard."
-- Ron to Mrs Weasley (GF31)
Urg the Unclean was a rebel leader during the goblin rebellions of the eighteenth century.
Ron Weasley jokingly refers to Urg as being one of many interchangeable goblin names that were possible answers to the third year History of Magic exam question about the Goblin Rebellions (GF31).
Urg was the subject of a "Famous Goblin" card (FW).
Other canon notes and references
Urg was also mentioned in the third W.O.M.B.A.T. test (which appeared on jkrowling.com in June 2007) as a possible answer to the question "Which of the following did NOT provoke one of the bloody goblin rebellions of the 17th and 18th centuries?" (JKR-W3).
According to the W.O.M.B.A.T. 3 test, Urg was a goblin activist (who might have been ducked in a pond by a gang of young wizards). Unless we get the answers to the test someday, the ducking cannot be considered canon.