king of Norway (1130–36), a ruthless sovereign whose feud with his fellow king Magnus IV the Blind over the Norwegian throne marked the beginning of a period of civil wars (1130–1240) during which the right to rule was constantly in dispute. Harald's weak character helped lay the foundation for the increasingly powerful role played by the aristocracy in the civil war period.

Harald arrived in Norway from Ireland in 1128, claiming to be a son of the Norwegian king Magnus III Barefoot (reigned 1093–1103). After Harald had passed an ordeal of walking over hot plowshares, Sigurd I Jerusalemfarer (Sigurd I Magnusson), Magnus III's son and reigning king, recognized him as his brother on the condition that Harald would not claim sovereignty during the lifetime of Sigurd or of his son Magnus (later Magnus IV the Blind). After Sigurd's death in 1130, Harald flouted the agreement and was accepted as king in half the kingdom, while Magnus ruled the rest of Norway.

Hostilities broke out between Harald and Magnus IV in 1134; Harald was initially defeated at Fyrileif and retreated to Denmark to obtain reinforcements. On returning to Norway, he captured Magnus in 1135, maimed and blinded him, and put him in a monastery. Harald was then sole ruler of Norway, but he was killed the following year by a pretender to the throne, Sigurd Slembi, who also claimed to be a son of Magnus III Barefoot.