Lord Stanley later 14th Earl of Derby 1846 Edward George Geoffrey Smith-Stanley, 14th Earl of Derby , KG, PC (29 March 1799 - 23 October 1869) was an English statesman, three times Prime Minister of the United Kingdom, and to date the longest serving leader of the Conservative Party. He was known before 1834 as Edward Stanley, and from 1834 to 1851 as Lord Stanley.