Óláfr Tryggvason, also called Olaf Tryggvason, (963 – September 9, 1000), was King of Norway from 995 to 1000. He was the son of Tryggve Olafsson, king of Viken, (Vingulmark and Ranrike), and the great-grandson of Harald Fairhair, first King of Norway. Olaf played an important part in the conversion of the Vikings to Christianity. He is said to have built the first church in Norway in 995 and to have founded the city of Trondheim in 997.