Þorkell inn hávi, also known as Thorkell the Tall or Thorkell the High, was a Jomsviking, a son of the Scanian chieftain Strut-Harald, a brother of Jarl Sigvaldi, commander of the Jomvikings and the stronghold of Jomsborg, on the Island of Wollin, while himself a notable lord.
In 1012, he and his men entered into the service of king Ethelred the Unready, whom they fought under in 1013 against the invasion of king Sveinn Forkbeard and his son Canute the Great. After the death of Sveinn, and the English attacks on the Danish invaders which drove his son to abandon the conquest, Ethelred's forces were turned against the Jomsvikings in his service. Thorkell's brother Henning was killed, and he went back to Denmark with a score to settle in England.
He was to return with the future king, in 1015, and the invasion's success meant he was proclaimed to be the Jarl of East Anglia, in 1017, after the coronation of Canute. Thorkell had been the childhood mentor of Canute, who has been trained among the Jomsvikings.
In 1021, though, Jarl Thorkell fell out with king Canute and departed for Denmark. He was soon reconciled with Canute again, who proclaimed him Jarl once more, of Denmark, although he disappeared in 1023. It is said by some that he spent the rest of his years as a wayward old soldier, seeking death in battle rather than abed.