Thorfinn had ruled alone in Orkney until the return in in about 1037 of his nephew Rognvald Brusason.

Rognvald had received the favor of King Magnus the Good, who has granted him Brusi's share of the islands and the third which Olaf Haraldsson had claimed after Einar's death.

Thorfinn agrees to this division, but presents the transfer of the third claimed by the Norwegian king as a gift to Rognvald in return for aid in Thorfinn's wars in the Hebrides and the Irish Sea.

King Sigtrygg Silkbeard had died in 1035 or 1036, and the kingship in Dublin had come to Echmarcach mac Ragnaill, who in 1038 is challenged by Imar mac Arailt and driven out.

This instability in Dublin can only have helped Thorfinn and Rognvald, who raid far and wide and establish their rule over some part of the lands around the Irish Sea.

They are said to have won a major victory beside Vattenfjord, perhaps Loch Vatten on the west coast of the Isle of Skye.

The Earls are said to have raided in England, with mixed success.

The Orkneyinga Saga says that a dispute between Thorfinn the Mighty, Earl of Orkney, and Karl Hundason began when Karl Hundason became "King of Scots" and claimed Caithness.

In the war that ensued, …

…Thorfinn defeated Karl in a sea-battle off Deerness at the east end of the Orkney Mainland.

Then, …

…Karl's nephew Mutatan or Muddan, appointed to rule Caithness for him, was killed at Thurso by Thorkel the Fosterer, who had been Thorfinn’s foster father.

Finally, …

…a great battle at Tarbat Ness on the south side of the Dornoch Firth ended with Karl defeated and fugitive or dead.

Thorfinn, the saga says, then marched south through Scotland as far as Fife, burning and plundering as he passed.

A later note in the saga claims that Thorfinn won nine Scottish earldoms.

The identity of Karl Hundason, unknown to Scots and Irish sources, has long been a matter of dispute, and it is far from clear that the matter is settled.

The most common assumption is that Karl Hundason was an insulting byname ("Churl, son of a Dog") given to Mac Bethad by his enemies.

Skene's suggestion that he was Donnchad mac Crínáin has been revived in recent years.

Lastly, the idea that the whole affair is a poetic invention has been raised.

Whoever Karl son of Hundi may have been, it appears that the saga is reporting a local conflict with a Scots ruler of Moray or …

…Ross.

Macbeth, who probably has a personal claim to the crown of Scotland through royal descent, in about 1031 had succeeded his father, Finlay, as moarmaer (provincial governor) of Moray.

His marriage to As the grandson of King Malcolm II, Macbeth is thus a cousin to Duncan I whom he succeeds, and probably also a cousin to Thorfinn the Mighty, Earl of Orkney and Caithness.

Some historians claim, however, that Macbeth was Thorfinn's half-brother rather than his cousin.

Much depends on whether Malcolm had three daughters or only two (one of whom married twice) - a point which is likely to remain uncertain.

When Cnut the Great came north in 1031 to accept the submission of King Malcolm II, Macbeth too submitted to him.

Some have seen this as a sign of Macbeth's power; others have seen his presence, together with Iehmarc, who may be Echmarcach mac Ragnaill, as proof that Malcolm II was overlord of Moray and of the Kingdom of the Isles.

Whatever the true state of affairs in the early 1030s, it seems more probable that Macbeth was subject to the king of Alba, Malcolm II, who died on November 24, 1034 at Glamis.

The Prophecy of Berchan, apparently alone in near contemporary sources, says Malcolm died a violent death, calling it a "kinslaying" without actually naming his killers.

Malcolm II's grandson Duncan (Donnchad mac Crínáin), later King Duncan I, had been acclaimed as king of Alba on November 30, 1034, apparently without opposition.

Duncan appears to have been tánaise ríg, the king in waiting, so that far from being an abandonment of tanistry, as has sometimes been argued, his kingship was a vindication of the practice.

Previous successions had involved strife between various rígdomna – men of royal blood.

Far from being the aged King Duncan of Shakespeare's play, the real King Duncan was a young man in 1034, and even at his death in 1040 his youthfulness is remarked upon.

Because of his youth, Duncan's early reign was apparently uneventful.

His later reign, in line with his description as "the man of many sorrows" in the Prophecy of Berchán, was not successful.

Strathclyde had been attacked in 1039 by the Northumbrians, and a retaliatory raid led by Duncan against Durham in 1040 turns into a disaster.

Later this year Duncan, leads an army into Moray, where he is killed by Macbeth on August 15, 1040, at Pitgaveny (at this time called Bothnagowan) near Elgin.

On Duncan's death, Macbeth becomes king.

No resistance is known at this time, but it would have been entirely normal if his reign were not universally accepted.

John of Fordun wrote that Duncan's wife fled Scotland, taking her children, including the future kings Malcolm III (Máel Coluim mac Donnchada) and Donald III (Domnall Bán mac Donnchada, or Donalbane) with her.

On the basis of the author's beliefs as to whom Duncan married, various places of exile, Northumbria and Orkney among them, have been proposed.

However, E. William Robertson proposes the safest place for Duncan's widow and her children would be with her or Duncan's kin and supporters in Atholl.