Haakon Sigurdarson (Haakon Jarl) (Old Norse: Hákon Sigurðarson, Norwegian: Håkon Sigurdsson) (c. 937 – 995) was the de facto ruler of Norway from about 975 to 995. Sometimes he is styled Hakon the Powerful (Old Norse: Hákon jarl hinn ríki).
Haakon was the son of Sigurd Haakonsson, Jarl of Lade and ruler of Trøndelag and Hålogaland. His mother was Bergljot Toresdatter, daughter of , Jarl of Møre. Adam of Bremen wrote that he was "of the stock of Ivar (possibly Ivar the Boneless) and descended from a race of giants". In the sagas, Haakon claimed descent from the divine lineage of Sæming, son of Odin. The Hakon Jarl Runestones in Sweden may refer to him.
Haakon became earl after his father was killed by King Harald Greycloak's men in 961. He warred with King Harald for some time, until he was forced to flee to Denmark and Harald Bluetooth. In Denmark he conspired with Harald Bluetooth against Harald Greycloak.
Haakon Jarl arranged the death of Harald Greycloak around 971 with the connivance of Harald Bluetooth, who had invited his foster-son to Denmark to be invested with new Danish fiefs. Civil war broke out between Haakon Jarl and the surviving brothers of Harald Greycloak, but Haakon proved victorious. After this, Haakon Jarl ruled Norway as a vassal of Harald Bluetooth, but he was in reality an independent ruler. For Harald, he attacked Götaland and killed its ruler Jarl Ottar. When Haakon was in Denmark, Harald Bluetooth forced him to accept baptism and assigned him clergymen to take to Norway to spread Christianity. When a favourable wind came for Haakon to leave, he commanded the clergymen to return ashore.