Question: Which British peer and politician born in 1734 was a great-grandson of the 1st Duke of Marlborough?
Context: John Spencer, 1st Earl Spencer (19 December 1734 – 31 October 1783) was a British peer and politician. Charles Lennox, 1st Duke of Richmond, 1st Duke of Lennox, 1st Duke of Aubigny (29 July 1672 – 27 May 1723) was an English nobleman and politician.  He was the illegitimate son of King Charles II of England and his mistress Louise de Kérouaille, Duchess of Portsmouth. Mary Osborne, Duchess of Leeds (1723 – 3 August 1764), born Lady Mary Godolphin, was a daughter of Henrietta Godolphin, "née" Churchill, 2nd Duchess of Marlborough, and Francis Godolphin, 2nd Earl of Godolphin, making her granddaughter to the powerful government trio during the reign of Queen Anne of Great Britain: the famous general and politician John Churchill, 1st Duke of Marlborough, and his wife Sarah, Duchess of Marlborough, through her mother; and Sidney Godolphin, 1st Earl of Godolphin, through her father. Henry Wellesley, 3rd Duke of Wellington (Apsley House, 5 April 1846 – 8 June 1900, Strathfieldsaye) was a British peer and Conservative Party politician.  He was the son of Lord Charles Wellesley and grandson of the 1st Duke of Wellington. Henrietta Ponsonby, Countess of Bessborough (16 June 1761 – 11 November 1821), born Lady Henrietta Frances Spencer (generally called Harriet), was the wife of Frederick Ponsonby, 3rd Earl of Bessborough, and mother of the notorious Lady Caroline Lamb.  Her father, John Spencer, 1st Earl Spencer, was a great-grandson of John Churchill, 1st Duke of Marlborough.  Her sister was Georgiana Cavendish, Duchess of Devonshire. King Edward III of England is the ancestor of many European monarchs (as well as the issue of many English Dukes, Earls and Viscounts) through his sons Lionel of Antwerp, 1st Duke of Clarence; John of Gaunt, 1st Duke of Lancaster; Edmund of Langley, 1st Duke of York and Thomas of Woodstock, 1st Duke of Gloucester.  All of Edward's legitimate children were by his wife Philippa of Hainault. Earl Spencer is a title in the Peerage of Great Britain that was created on 1 November 1765, along with the title Viscount Althorp, of Althorp in the County of Northampton, for John Spencer, 1st Viscount Spencer.  He was a member of the prominent Spencer family and a great-grandson of the 1st Duke of Marlborough.  Previously, he had been created Viscount Spencer, of Althorp in the County of Northampton, and Baron Spencer of Althorp, of Althorp in the County of Northampton, on 3 April 1761. Don Joaquín Baldomero Fernández-Espartero y Alvarez de Toro, 1st Prince of Vergara, 1st Duke of la Victoria, 1st Duke of Morella, 1st Count of Luchana, 1st Viscount of Banderas (27 February 17938 January 1879) was a Spanish general and politician, who served as the Regent of Spain.  He also served Prime Minister of Spain three times.  He was associated with the radical (or progressive) faction of Spanish liberalism and would become their symbol and champion after taking credit for the victory over the Carlists during 1839.  His noble title, "Duke of La Victoria" was granted by Isabella II to him as a result.  The title Prince of Vergara was granted to him by King Amadeo of Spain during 1870. Robert Spencer, 4th Earl of Sunderland (24 October 1701 – 15 September 1729) was a British peer from the Spencer family, the son of the Whig politician, Charles Spencer, 3rd Earl of Sunderland.  His mother was Lady Anne Churchill, the daughter of John Churchill, 1st Duke of Marlborough and Sarah Churchill, Duchess of Marlborough.  Known as Lord Spencer between 1702 and 1722, he succeeded to the Earldom after his father's death in, but died in 1729 with no children.  Therefore, his brother, Charles, became 5th Earl of Sunderland, and subsequently 3rd Duke of Marlborough after the death of his aunt, Henrietta Godolphin ("née" Churchill), 2nd Duchess of Marlborough. James FitzJames, 1st Duke of Berwick, 1st Duke of Fitz-James, 1st Duke of Liria and Jérica (21 August 1670 – 12 June 1734) was an Anglo-French military leader, illegitimate son of King James II of England by Arabella Churchill, sister of the 1st Duke of Marlborough.  Berwick was a successful general in the pay of Louis XIV of France.
Answer: John Spencer, 1st Earl Spencer