Castlereah (kas'-sl-ra), Robert Stewart, Lord. Eldest son of the Marquis of Londonderry. Born in 1769. At an early period Castlereah entered into public life, and was appointed keeper of the signet, or privy seal, in Ireland in 1797. President of the Board of Control in 1802; secretary of war in 1805. A difference having arisen between him and his colleague, Mr. Canning, a duel was the consequence, and both quitted office. During Lord Liverpool's administration, Lord Castlereah again became a member of the government as foreign secretary, and concluded the Treaty of Paris in 1814. Castlereah remained in office the remainder of his life, which was ended by suicide in 1822.