Gunthor

Gunthor is a member of the Stone Crows, one of the hill tribes of the Mountains of the Moon recruited by Tyrion Lannister to fight for him in the initial stages of the War of the Five Kings in exchange for gold, weaponry and armor the hill tribes could employ against House Arryn.

Season 1
Tyrion reports to his father and his uncle that Ulf, of the Moon Brothers, is demanding blood money from Shagga, of the Stone Crows. Shagga, Gunthor and a third Stone Crow had killed a Moon Brother after the latter stabbed a Stone Crow over a sausage. "Baelor"

In the books
In the books, Gunthor, son of Gurn, also meets Tyrion and Bronn and the Mountains of the Moon. However, instead of departing with Tyrion, Gunthor stays behind at the Mountains to rally the members of the hill tribes.