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:
- LONDONDERRY, EARLS AND MARQUESSES OF, 1911 Encyclopedia Britannica; [1] (http://22.1911encyclopedia.org/L/LO/LONDONDERRY_ROBERT_STEWART_2ND_MARQUESS_OF.htm)