A Mormaer was literally a High Steward of one of the ancient Celtic provinces of Scotland, but in Latin documents the word is usually translated as 'Comes', which means Earl.
Shakespeare's famous tragedy Macbeth is based upon his life, but is not historically accurate. In the play, Macbeth and his wife murder the aged King Duncan when he comes to visit them in their castle. In reality, Macbeth killed Duncan, who was about 39, in battle, and made himself king instead.
Macbeth's marriage to Kenneth III's granddaughter Gruoch strengthened his claim to the throne. In 1045, Macbeth defeated and killed Duncan I's father Crinan at Dunkeld.
His reign was for the most part peaceful, and he was known for his generosity to the Church. He made a pilgrimage to Rome in 1050, 'scattering money like seed'.
Seven years later, on 15 August 1057, he was killed at the Battle of Lumphanan in Aberdeenshire by Duncan's eldest son, Malcolm Canmore.