Domhnall I, Earl of Mar

Domhnall I, Earl of Mar, also known by the name Domhnall mac Uilleim (Anglicized as "Donald, William's son"), was the seventh known mormaer of Mar in medieval Scotland, ruling from the death of his father, Uilleam of Mar, in 1276 until his own death sometime between 1297 and 1302. If Gille Críst is excluded, Domhnall I is considered the sixth mormaer or Earl of Mar.

In 1284, he joined with other Scottish noblemen who acknowledged Margaret of Norway as the heir to King Alexander III. Domhnall was later a strong supporter of the Bruce cause during the crisis of the late 13th century. He was at Norham in 1292, probably in the camp of Robert de Brus, then Earl of Carrick.