Robert Stewart was a Scottish nobleman who lived during the 18th and 19th centuries. He was known for his political career, serving as the Chief Secretary for Ireland and later as the Chancellor of the Exchequer. Stewart was also a key figure in the Act of Union 1800, which united Great Britain and Ireland. He was eventually elevated to the peerage as Viscount Castlereagh and later as the Marquess of Londonderry. Stewart played a significant role in European diplomacy during the Napoleonic Wars and was involved in the Congress of Vienna, where he worked to establish a lasting peace in Europe. His contributions to British politics and international relations have left a lasting impact on history.