Robert Stewart (1739-1821) was the father of the famous politician Lord Castlereagh.
He was regularly promoted through the ranks of the peerage of Ireland:
- Baron Londonderry (1789)
- Viscount Castlereagh (1795)
- Earl of Londonderry (1796) - on reaching this rank, his son took Viscount Castlereagh as a courtesy title.
- Marquess of Londonderry (1816)
Reference
- LONDONDERRY, EARLS AND MARQUESSES OF, 1911 Encyclopedia Britannica; [1]