The Lord of the Dúnedain was a title that could in principle be taken by any lord of the Númenóreans or their descendants in Middle-earth. In practice, though, it is only ever used as an equivalent to 'Chieftain of the Dúnedain', the style used by the Heirs of Isildur after the fall of Arthedain. The title is only recorded as being used by Aragorn II, the last of the Chieftains, but doubtless it applied equally to any of his forebears.