Duncan was the grandson of King Malcolm II (ruled 1005-34), who irregularly made him ruler of Strathclyde when that region was absorbed into the Scottish kingdom (probably shortly before 1034). Malcolm violated the established system of succession whereby the kingship alternated between two branches of the royal family. Upon Malcolm's death, Duncan succeeded peacefully, but he soon faced the rivalry of Macbeth, Mormaor (subking) of Moray, who probably had a better claim to the throne. Duncan besieged Durham unsuccessfully in 1039 and in the following year was murdered by Macbeth. Duncan's elder son later killed Macbeth and ruled as King Malcolm III Canmore (1058-93).



Duncan married a daughter of Siward, Danish Earl of Northumbria (a Viking) and his first wife Elfleda of Northumbria; Siward, d. 1055, is son of Earl Berne of the Royal House of Denmark. Duncan succeeded his maternal grandfather,
Malcolm II, in 1034 ("the first example of inheritance of the Scottish throne in the direct line"); previously he was King
of Cumbria (ruling from Strathclyde){-Encycl.Brit.,1956,7:736,20:146}. He was slain by his own general, Macbeth.
His male line ruled Scotland until the death of Alexander III in 1286. Duncan is the first king of the House of Atholl.

Killed by MacBeth, his successor.
He was slain by his cousin Macbeth, whose wife Gruoch was a claiment
to the throne. His life was forfeited according to the old Gaelic system
whereby a king expected to be slain by his rightful successor, unless he
could manage to kill him first, a relic from Pagan times...that was
written about by William Shakespeare in "MacBeth".

References: [AR7],[Paget1],[RFC],[Weis1],[BurkeP]