He was born around 850 AD and was the son of Olaf the White, King of Dublin, and Aud the Deep-minded, who was the daughter of Ketil Flatnose.
[1] Together Thorstein and Sigurd waged a series of campaigns in Caithness, Sutherland, Ross, Moray, and a number of other regions, eventually receiving tribute from half of Scotland.
[3] However, the Scottish chieftains plotted against Thorstein, and he was killed; the exact nature of his death is unknown but it probably took place around 880 or 890.
After Thorstein's death Aud left Caithness, sojourning for a while in Orkney before settling with other members of her clan in Iceland.
Thorstein and Thurid had a son, Olaf Feilan, and a number of daughters, including Groa, Thorgerd, Olof, Osk, Thorhild, and Vigdis.