 Óláfr Guðrøðarson ( IPA : [ <unk> <unk> ] ) , commonly known in English as Olaf the Black , was a mid 13th century sea @-@ king who ruled the Isle of Man ( Mann ) and parts of the Hebrides . Óláfr was the son of Guðrøðr Óláfsson , King of the Isles , King of Dublin , and his wife Finnguala , granddaughter of Muirchertach Mac Lochlainn , High King of Ireland , King of Cenél nEógain . Óláfr was a younger son of his father ; his elder brother Rögnvaldr more than likely had a different mother . According to the Chronicle of Mann , Guðrøðr appointed Óláfr as heir since he had been born " in lawful wedlock " . Whether or not this is the case , on Guðrøðr 's death in 1187 the Manxmen instead appointed Rögnvaldr as king , as he was a capable adult and Óláfr was a mere child . Rögnvaldr ruled the Crovan dynasty 's island @-@ kingdom for almost 40 years , during which time the half @-@ brothers vied for the kingship . 
