Not much is known about Uilosdîn's life, except that he is a Dúnedain and one of the most trusted of Halbarad's men. 

He was born and raised in one of the small villages flowing before the town of 
Dolindîr in North Downs. After years, the forces of Angmar came down from the North to invade the villages. They burned and killed whoever before them. They were grim and the day was dark. Many died that day, including his mother. When the orcs returned to their master in the great fortress of Angmar. They were scattered and homeless. His father, Annûn​lach took him to Esteldín, torn and worn fortress once was the town of Dolindîr. There, many took refuges and these people were incorporated into the Ranger Military. Not only themselves... but also their sons, and their sons, and so on, to serve as rangers. He was such a son. 

Early in life, he became well skilled in both bow and sword skills. He joined in several patrols in Southern Angmar, handled vague pursuits in the dark. He always wondered what lies in the heart of Carn Dûm and he kept his passion for revenge deep in heart.

Etymology:
Uilosdîn is a Sindarin word for 'White silence'.​
Annûn​lach is a Sindarin word for 'Leaping flame of the West'.