Ulf

Ulf is the leader of the Moon Brothers, 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 is demanding blood money from Shagga. Shagga, Gunthor and a third Stone Crow killed a Moon Brother after the latter stabbed a Stone Crow over a sausage. "Baelor"

In the books
In the books, Ulf, son of Umar, is also the leader of the Moon Brothers. He fights for the Lannisters during the Battle of the Green Fork and perishes.