Titles:
King of Strathclyde (1018 - 1034)
King of Scots (1034 - 1040)

King Duncan I (Donnchad mac Crínáin) (August 15, 1001 – August 15, 1040) was King of Scots, a son of Crinan the Thane de Mormaer, lay abbot of Dunkeld, and Princess Bethoc of Scotland. He became King of Scotland in succession to his maternal grandfather Malcolm II of Scotland in 1034, having previously ruled as rex Cumbrorum in the Kingdom of Strathclyde. His accession is said to be "the first example of inheritance of the Scottish throne in the direct line", as opposed to the previous tanistry system.

Duncan I was known as Duncan The Gracious, a title that was not entirely complimentary. His uncaring approach to matters of state made him unpopular both with his subjects and the nobility. Not a strong ruler, he is chiefly known today through his connection with King Macbeth, which has been immortalized by William Shakespeare. The feud between these two when princes originated probably in a dispute over the succession to the throne; its details, however, are obscure, and the only fact which can be stated with any certainty is that Duncan I was slain in battle by Macbeth, near Elgin, Moray, on August 15, 1040.

In 1039, Duncan I marched south to besiege Durham, Northumbria, England, but was defeated with heavy losses. He also attempted to seize control of Moray, but was twice defeated by the Earl of Orkney's son, Thorfinn, before being killed in battle. He was killed at Bothnguane and buried at Iona.
Details of Duncan I's marital life are a matter of debate among historians. The Scottish Regnal List I calls his wife Suthen, and John of Fordun calls her a kinswoman of Siward Biornsson, Earl of Northumbria. The United Kingdom's official history of the monarchy states that she was Siward's cousin.

Two of Duncan I's sons, Malcolm III Canmore (1058–93) and Donald Bane, were afterwards Kings of the Scots. Another son, Máel Muire, was the father of Matad, Mormaer of Atholl, whose own son Harald Maddadson ruled in Orkney.