Mac Bethad mac Findláech, known as Macbeth (Gaelic for "Son of Life") c. 1005–August 15, 1057 was the king of Scotland from August 14, 1040 to August 15, 1057 and the last Celtic king of Scotland.

His exact relationship to the Kings of Scotland is uncertain; only the late 13th century Chronicle of Huntingdon calls him nepos (nephew or grandson) of King Malcolm, and from context this king Malcolm appears to be Malcolm III, not Malcolm II, who is sometimes identified as Macbeth's grandfather. He did however marry Gruoch; better known to history as Lady Macbeth, a granddaughter of Kenneth III of Scotland, and daughter of the prince Bodhe. In 1031, according to the Anglo-Saxon chronicle, Macbeth was one of three Scottish kings who submitted to Canute.

Macbeth formed an alliance with Thorfinn , Earl of Orkney, son of Malcolm II's youngest daughter, and took up arms against Duncan. Duncan died fighting them in battle near Elgin on August 14, 1040.

Macbeth was a strong king and ruled over a kingdom stable enough for him to be able to leave for several months on a pilgrimage to Rome. He instituted a new form of law and order in Scotland. His reign was noted as a time of prosperity. However, in 1054, Malcolm Canmore, Duncan's son, began his campaign for the throne with the assistance of Siward , Earl of Northumbria, by capturing the south of Scotland. Macbeth was killed by Malcolm's forces at a battle near Lumphanan and the throne passed to Macbeth's stepson, Lulach, in August, 1057.

Macbeth was buried on Iona, the traditional burial place of Scottish Royalty at that time. William Shakespeare's play Macbeth is loosely inspired by his life.