Castlereagh,
Viscount (Robert Stewart) 2d Marquis of Londonderry 1769-1822; Brit. statesman, born in Ireland
See Castlereagh in American Heritage Dictionary 4
(kăsˈəl-rāˌ), Viscount. Title of Robert Stewart, Second Marquis of Londonderry. 1769-1822.
British politician who as chief secretary for Ireland (1798-1801) was able to quell the 1798 rebellion and form a political union between Ireland and Great Britain (1800).