Donald Mormaer, 8th Earl of Mar was born around 1302 in Saline, Fife, Scotland. He was regent of Scotland for the young King David II, son of Robert the Bruce.

Following the invasion of Edward Balliol, with the support of Edward III, Mar led the Scots loyalists to defeat at the Battle of Dupplin Moor in 1322 and died in battle.

Through his marriage to Isabella Stewart they had a single daughter, Margaret de Mar Countess de Mar.