Magnús Þorsteinsson (contemporary), Icelandic businessman; chairman and boardmember of several large businesses
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Klængur Þorsteinsson (1102–1176), Icelandic Roman Catholic clergyman; bishop of Iceland 1152–76
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Pétur Þorsteinsson (born 1955), Icelandic priest and neologist; leader of an Icelandic language movement
According to the legend, Loftur Þorsteinsson tried to obtain the legendary grimoire Rauðskinna from the dead Bishop Gottskálk grimmi Nikulásson of Holar by the use of magic.