Rosebery (1847-1929) was a clever but indolent young man, possibly gay, sent down from Oxford before his Finals for owning racehorses. He married a Rothschild heiress and bankrolled Gladstone’s Midlothian campaign, after which he turned down several junior offices in Gladstone’s 1880 government. His reward was the Foreign Office in 1886, when the withdrawal of the Whigs had opened up senior places. After serving as the first Chairman of the London County Council, he returned to the Foreign Office in 1892, then when Gladstone retired in 1894 he was chosen prime minister by Queen Victoria over the claims of Sir William Harcourt (1823-1904).
Rosebery was prime minister for only 16 months, presiding over a quarrelsome government; his only substantial achievement was to own the Derby winner twice in 1894 and 1895, a feat he repeated in 1905. He retired from the Liberal leadership in 1896, to become an ineffectual centrist elder statesman, surviving into the new world of 1929 and dying to the sound of the Eton Boating Song. He should rank near the bottom of the list, though he did little damage.