John Mor Tanaisdear (Tanister)

The word 'Tanister' comes from 'an tanaise' meaning 'heir designate'.

John Mar, a son of Good John and a younger brother of Donald, Lord of the Isles from 1387 to 1422, although designated, never did succeed to the title.

At this time the English kings were aspiring to be Lords of Ireland, and John did homage to Richard II in Gaelic at Drogheda in 1395. At about this time he made an advantageous marriage with the heiress to the Glens of Antrim, Margery Bisset, becoming known as John Mar of Dunivaig and the Glens. From him are descended the MacDonnells, Earls of Antrim.

John Mar Tanister was killed on Islay in 1427 and probably buried at Finlaggan.