Harald Greycloak, eldest surviving son of Eric Bloodaxe, ruled western Norway (c. 961–970) with his brothers under Danish patronage, destroying rival kings until Danish treachery destroyed him in turn.
Harald Greycloak led the sons of Eric Bloodaxe back from exile to claim their grandfather Fairhair's kingdom, finally winning it when Haakon the Good fell at Fitjar around 961. The brothers ruled the western coast harshly by saga account — killing the petty kings of the Uplands and Trøndelag's jarl, and breaking sacrifices as baptised kings among heathen subjects.
The nickname came, Snorri says, from a consignment of grey sheepskin cloaks he made fashionable to help Icelandic merchants. His Danish patron Harald Bluetooth turned on him around 970: lured to the Limfjord with promises of Danish fiefs, he was ambushed at Hals and killed, and Norway passed to Jarl Håkon under Danish lordship.
Harald was born around 935 to Eric Bloodaxe and Gunnhild, the saga tradition's arch-schemer among queens. His father's expulsion from Norway and death in England (at Stainmore, 954) left the brood of Eirikssons at the Danish court, where Harald Bluetooth stood godfather to their ambitions against Haakon the Good.
The brothers were baptised in England or Denmark — making them, after Haakon, the second Christian generation to claim Norway — and spent the 950s raiding their homeland's coasts in Danish-backed attempts that Haakon threw back at Avaldsnes, Rastarkalv, and finally, at the price of his own life, at Fitjar.
The saga picture — Heimskringla and Fagrskinna, written 250 years later — is of the ablest of a hated brood: a hard fighter from his youth in the eastern Baltic raids, more decisive than his brothers, but ruling in famine years that Norse memory blamed on the kings' impiety. The verses of contemporary skalds, quoted by Snorri, honour his generosity and his war-luck, the two virtues a Norse king could not lack.
His mother Gunnhild dominates the tradition's explanation of the brothers' cruelty; how much of that is history and how much the sagas' need for a villainess is genuinely unknowable. What the tradition concedes even in hostility is that Harald and his brothers destroyed everyone the sagas name as their rivals — until the ally behind them decided the tool had grown too independent.
From about 961 Harald was the leading king among his brothers, holding the west coast heartland while Danish power stood behind and above them. The saga catalogue of their reign is a list of eliminations: King Tryggve Olafsson and King Gudrød Bjørnsson of the Vestfold line killed, Jarl Sigurd of Lade burned in his hall — each removal clearing the board, and each making new enemies, most fatefully Sigurd's son Jarl Håkon.
Around 970 Håkon and Harald Bluetooth closed the trap: an invitation to Denmark, fiefs in the offing, and at Hals in the Limfjord a battle arranged in advance, where Harald fell to Gold-Harald Knutsson — who was then himself promptly destroyed by Håkon, leaving the jarl to rule Norway as Denmark's man. Gunnhild and the surviving sons fled to Orkney; the age of the Eirikssons was over.
Harald's fall reset the Norwegian kingship twice over: it proved Denmark could make and unmake Norway's kings, and it left the Fairhair claim dormant until Olaf Tryggvason — son of the Tryggve whom Harald had killed — returned in 995 to reclaim it. The pattern of exile, Danish patronage, and violent return that Harald rode to power outlived him by a century.
For the church's memory he remained ambiguous: a baptised king who broke heathen altars but is credited with no mission, remembered chiefly for hunger and hard rule — the contrast against which the sagas built the missionary reigns of the two Olafs.