Alexander Comyn, 2nd Earl of Buchan (died 1289) was a Scoto-Norman magnate who was one of the most important figures in the 13th century Kingdom of Scotland. He was the son of William Comyn, jure uxoris Earl of Buchan, and Marjory, Countess of Buchan, the heiress of the last native Scottish Mormaer of Buchan, Fergus. He was the chief counsellor of Alexander III, King of Scots for the entire period of the king's majority and, as Scotland's leading magnate, played a key role in safeguarding the independence of the Scottish monarchy. During his long career, Alexander Comyn was Justiciar of Scotia (1258–89), Constable of Scotland (1275–89), Sheriff of Wigtown (1263–66), Sheriff of Dingwall (1264–66), Ballie of Inverie (in Knoydart) and finally, Guardian of Scotland (1286–89) during the first i