Robert Jenkinson, 2nd Earl of Liverpool

Liverpool held office for nearly fifteen years, longer than any prime minister since, largely by managing a cabinet of stronger personalities: Castlereagh at the Foreign Office, then Canning, with Peel at the Home Office and Wellington. He kept bitter rivals, Canning and Castlereagh had fought a duel in 1809, working together, and in the 1820s let liberal Tories reform tariffs and criminal law. Once his stroke removed him in 1827, the coalition broke up within months, which says everything about his role.