Complex sentence: The Tory Leader of the House of Commons until 1822, when he committed suicide, was Robert Stewart, Viscount Castlereagh who inherited his father's Irish peerage and became the 2nd Marquess of Londonderry in 1821.
Split into simpler sentences: The Tory Leader of the House of Commons until 1822, when he committed suicide, was Robert Stewart. He was known by the courtesy title of Viscount Castlereagh, until he inherited his father's Irish peerage and became the 2nd Marquess of Londonderry in 1821.