Donnchad mac Crinain (
Modern Gaelic:
Donnchadh mac Crìonain; anglicised as
Duncan I, and nicknamed
An t-Ilgarach, "the Diseased" or "the Sick"; ca. 1001 – 14 August 1040) was king of
Scotland (
Alba) from 1034 to 1040. He is the historical basis of the "
King Duncan" in
Shakespeare's play
Macbeth.