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),^[1] 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 Alexander III. In 1284 he joined with other Scottish noblemen who acknowledged Margaret of Norway as the heiress to King Alexander.^[2] He died sometime after 10 July 1289.

Alexander had at least nine children with his wife, Elizabeth, daughter of Roger de Quincy, 2nd Earl of Winchester:

• John Comyn, 3rd Earl of Buchan, Alexander's successor as Earl of Buchan
• Roger
• Lord Alexander Comyn, sheriff of Aberdeen, married Joan, sister of William le Latimer, and had issue. Henry de Beaumont would claim the Earldom of Buchan through marriage to their daughter, Alice.
• Lord William Comyn, Provost of St. Mary's Church, St. Andrews
• Lady Marjorie Comyn, m. Patrick Dunbar, 8th Earl of Dunbar
• Lady Agnes Egidia Comyn, m. Maol Íosa III, Earl of Strathearn
• Lady Elisabetha Comyn, m. Gilbert de Umfraville, 1st Earl of Angus
• Lady Elena Comyn, m. Sir William de Brechin
• Lady Annora Comyn, m. Nicholas de Soules