Archibald Primrose, 5th Earl of Rosebery
Becoming involved in politics, he became a Liberal, and was involved in Gladstone's Midlothian campaign, which brought the Liberals back into power in 1880.  In the Liberal administration that followed, Rosebery served in junior offices, including that of Under-Secretary of State for the Home Department, before entering the Cabinet as Lord Privy Seal in March 1885.