John Stewart, 1st Earl of Atholl – Wikipedia

Life. He was the oldest child of Joan Beaufort, widow of James I of Scotland, and her second husband Sir James Stewart, the Black Knight of Lorn.. He was created Earl of Atholl in around 1457, the first earl of the eighth creation of the title. He is believed to have had a hand in suppressing the rebellion of John Macdonald, 11th Earl of Ross, the last of the Lords of the Isles.

https://en.wikipedia.org/wiki/John_Stewart,_1st_Earl_of_Atholl