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. During his long career, Alexander 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 interregnum following the death of King Alexander III. He died sometime after 10 July 1289.