King of Scots; Before his accession to the Scottish throne, he was ruler of the kingdom of Strathclyde. The Scottish nobleman, Macbeth (d. ca. 1057), who ruled the kingdom of Moray and served as Duncan's General, killed Duncan and became King of Scotland
Macbeth era al parecer tambien primo de Duncan, al ser hijo de Anleta, hermana de su madre.
http://www.royal.gov.uk, site oficial, dice que contrariamente a la tragedia de Sheakespeare, Macbeth mato a Duncan en batalla. El haberse casado con la nieta de Kenneth III fortalecio sus aspiraciones al trono.
http://www.scotsheritage.co.uk/Timeline/Timeline2.htm1040 By the Celtic rule of succession to the throne, Duncan was a usurper. The rightful " tanist " or heir of Malcolm II was his cousin's descendant, Lulach. Lulach's stepfather, Macbeth, mormaor or earl of Moray, slew Duncan in battle near Elgin and ruled on behalf of his step-son. 1057 With the help of Siward, Earl of Northumbria, Malcolm III (nicknamed Canmore or " Big Head "), son of Duncan, recovered his father's throne, slaying Macbeth in battle at Lumphanan in Aberdeenshire.
By establishing the supremacy of the Scots over all rivals, the battle of Carham closed an epoch. The union of Scotland under Duncan, however, was probably just a loose confederacy of peoples of different races, languages and customs. Contact with the administration of SaxonEngland suggested this to the Kings of Scots as the model on which it was desirable to organise their) kingdom. Having broken first the Celtic custom of succession to the throne, and thus united Strathclyde with Scotland, theynext became committed, by the influence of St. Margaret, to a premature attempt to anglicise the Court and theCeltic Church. This roused such opposition as to endanger the unity of the kingdom. (sigue en notas de su hijo Malcolm)