Sigurd the Dane, also known as Siward or Siward “Digera” (the Stout), was an English nobleman in the eleventh century, and the earl of Northumbria.

Siward was a descendant of the Danish royal family, whose ancestors had arrived in England a few generations earlier as part of the Norse colonization of Britain. He was the hereditary ruler of Northumbria.

He served as a general to Harthacanute and Edward the Confessor, and gained great renown for his skills as a soldier. He was related to the Scottish royal family, and was either the uncle or the brother-in-law of Malcolm Canmore (one text erroneously calls him his grandfather). Following Macbeth's defeat of Malcolm's father King Duncan I in 1040, the infant Malcolm was sent to Northumbria to be guarded by Siward. In 1053, Edward the Confessor agreed to assist the now adult Malcolm in taking the throne of Scotland, and designated Siward as leader of the English army. Siward's first incursion met with limited success, capturing the fortress Dunsinane in 1054, but Macbeth was not decisively defeated until 1057 at Lumphanan. One of Siward's own sons, Osberne, was killed during the campaign in Scotland.

Malcolm's son King David I would later marry Siward's granddaughter Matilda. Siward's descendants also included James I of England, although this was not known during James' time.
Siward and Osberne (Young Siward) are both characters in William Shakespeare's Macbeth.