He is also called "Ketil Krok" [Hook], possibly meaning he was stoop-shouldered.
From Snorre Sturlasson: Saga of Harald Hardråde:
"102. OF OLAF HARALDSON'S EXPEDITION TO NORWAY. Olaf, the son of King Harald Sigurdson, sailed with his fleet from England from Hrafnseyr, and came in autumn to the Orkney Isles, where the event had happened that Maria, a daughter of Harald Sigurdson, died a sudden death the very day and hour her father, King Harald, fell. Olaf remained there all winter; but the summer after he proceeded east to Norway, where he was proclaimed king along with his brother Magnus. Queen Ellisif came from the West, along with her stepson Olaf and her daughter Ingegerd. There came also with Olaf over the West sea Skule, a son of Earl Toste, and who since has been called the king's foster-son, and his brother Ketil Krok. Both were gallant men, of high family in England, and both were very intelligent; and the brothers were much beloved by King Olaf. Ketil Krok went north to Halogaland, where King Olaf procured him a good marriage, and from him are descended many great people. ..."
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