Lulach mac Gille Coemgáin (Modern Gaelic: Lughlagh mac Gille Chomghain, known in English simply as Lulach, and nicknamed Tairbith, "the Unfortunate" and Fatuus, "the Simple-minded" or "the Foolish"; before 1033 – 17 March 1058) was King of Scots between 15 August 1057 and 17 March 1058.
Lulach was the son of Gruoch of Scotland, from her first marriage to Gille Coemgáin, Mormaer of Moray, and thus the stepson of Macbeth (Mac Bethad mac Findlaích). Following the death at the Battle of Lumphanan of Macbeth on 15 August 1057, the king's followers placed Lulach on the throne. He has the distinction of being the first king of Scotland of whom there are coronation details available: he was crowned, probably on 8 September 1057 at Scone. Lulach appears to have been a weak king, as his nicknames suggest, and ruled only for a few months before being assassinated and usurped by Malcolm III (Máel Coluim mac Donnchada).