Donald Sage Mackay, Baron Mackay of Drumadoon, PC was a British judge of the Supreme Courts of Scotland, and a Lord Advocate, the country's senior Law Officer. He was also one of five additional Lords of Appeal in the House of Lords, where he sat as a crossbencher.

His Majesty's Advocate, known as the Lord Advocate, is the principal legal adviser of both the Scottish Government and the Crown in Scotland for civil and criminal matters that fall within the devolved powers of the Scottish Parliament. The Lord Advocate provides legal advice to the government on its responsibilities, policies, legislation and advising on the legal implications of any proposals brought forward by the government. The Lord Advocate is responsible for all legal advice which is given to the Scottish Government.