Borgthaur was a king of his small snaga kingdom located between the Misty Mountains and the Blue Mountains during the Third Age.
When Murazor of Angmar attacked Borgthaur's kingdom, Borgthaur escaped to Isengard, where he started working as an orc overseer. Once, when he went across the caverns of Orthank, he saw a sitting uruk. Borgthaur came to the uruk and hit him by a wheep. The uruk roared and started chasing Borgthaur across the caverns. Borgthaur knew Isengard very well, so he ran out from the caves up to the tower. Then, he left Isengard and went to Mordor. Later, he fought in the second battle of Osgiliath and in the battle of the Pelennor Fields. He, with a small mordor orc band, was at Grond when it broke the Gate of the City of Kings.