http://en.wikipedia.org/wiki/Robert_Gascoyne-Cecil%2C_3rd_Marquess_of_Salisbury

Prime Minister for 13 years. -------------------- http://en.wikipedia.org/wiki/Robert_Gascoyne-Cecil,_3rd_Marquess_of_Salisbury

Robert Arthur Talbot Gascoyne-Cecil, 3rd Marquess of Salisbury, KG, GCVO, PC (3 February 1830 – 22 August 1903), known as Lord Robert Cecil before 1865 and as Viscount Cranborne from 1865 until 1868, was a British Conservative statesman and thrice Prime Minister, serving for a total of over 13 years. He was the first British Prime Minister of the 20th century and the last Prime Minister to head his full administration from the House of Lords.

Salisbury is seen as an icon of traditional, aristocratic conservatism. The Conservative historian Robert Blake considered Salisbury "the most formidable intellectual figure that the Conservative party has ever produced". The Conservative historian Maurice Cowling claimed that "The giant of conservative doctrine is Salisbury".

Not long before his death in 1967, Clement Attlee (Labour Party Prime Minister, 1945–1951) was invited to Chequers by Prime Minister Harold Wilson and was asked who he thought was the best Prime Minister of his lifetime. Attlee immediately replied: "Salisbury".