The Jacobite title of Duke of Mar was conferred on John Erskine, 6th/23rd Earl of Mar, by the Jacobite pretender James III and VIII. He was created Duke of Mar, Marquess Erskine or Marquess of Stirling, Earl of Kildrummie, Viscount of Garioch and Lord Alloa, Ferriton and Forrest in the notional Peerage of Scotland in 1715, with the same remainder as his Earldom, i.e. to heirs-general. The Duke's attainder by the government of the Hanoverian George I the following year was, of course, not recognised in Jacobite circles. He was further created Earl of Mar in the Peerage of England in 1717 and Duke of Mar in the Peerage of Ireland in 1722. These titles had the ordinary remainder to heirs male of the body, and became extinct on the death of the grantee's son in 1766. The other titles, such as they are, remain extant, although they are not recognised by the British or any other government and have not been claimed or used by their holders since the eighteenth century.
(numbering of Earls ignores the attainder of 1716, and is therefore different from that currently used)