 Sigtrygg may have succeeded his paternal half @-@ brother Glúniairn as king of Dublin in 989 , but it is just as likely his rival Ivar of Waterford came to power in the city then . The Irish annals record little information about Sigtrygg , his family or Dublin during these first five years of his reign . Benjamin Hudson claims this was because of the arrival of the future King of Norway , Olaf Tryggvason , who took up residence in Dublin for a few years after marrying Sigtrygg 's sister Gytha . Tryggvason had met Gytha while raiding along the coasts of the Irish Sea . The presence of a powerful Viking leader in Dublin was a deterrent to Irish raids , and Trygvason may have weakened Sigtrygg 's foes by plundering them . 
