I would say Napoleon was the greatest of them all. He went from being a mere member of an impoverished Corsican noble family to being leader of all of France, a position he attained by his indefatigability, his brilliant genius and his strength of will. He crowned himself Emperor in a land that had rid itself of kings. He brought order and progress, and mobilised the entire country for his ambitions. He won many glorious victories, and subdued the tired old autocrats and reactionaries throughout the continent. He ended the French Revolution and merged what was good about it with what was good about monarchy, order and tradition. He made France's education system the best in Europe, made her armies the greatest in Europe and made her power unchallenged for many years. At long last, he was defeated by his enemies and exiled to the island of St. Helena, but the legacy of this giant of a man continued to loom large over the continent. It was because of Napoleon that the French Revolution did not destroy itself entirely. It is thanks to Napoleon that nationalism arose throughout Europe. It is thanks to Napoleon that the militaries of the European states were forced to reform themselves, becoming bigger and more sophisticated, until finally they had the means with which to destroy each other a hundred times over, and millions sacrificed in great and terrible wars.
After Napoleon, I would say Bismarck was the greatest leader of the 19th century. Bismarck single-handedly manipulated all of Europe and achieved what German liberals had tried and failed to achieve for years a - united Germany, and yet under control of reactionary conservatives in Prussia, not dangerous, utopian liberals. Under him, Prussia won war after war - against Denmark, against Austria, against France.
There are other greats. Metternich, for example, created the Concert of Europe which held revolution at bay on the continent for many decades. Napoleon III claimed the mantle of the legacy of his great uncle before him and achieved a brief period of greatness for France before being defeated by democratic elements within his own country and by Bismarck's Prussia. Garibaldi set aflame the Italian Peninsula with nationalism and created a united Italy together with Cavour and Mazzini.
And of course, we must not neglect our own native Britain. I believe that William Pitt the Younger was one of our greatest Prime Ministers, putting in place measures that allowed us to win the Napoleonic Wars, including the unpopular income tax, which we have been stuck with ever since. (Sorry, libertarians.) Robert Peel did away with the disastrous Corn Laws and as such sacrificed his Tory Party for the good of the country, creating a completely new party in the process, the Liberals. Gladstone was a brilliant Chancellor and Prime Minister, bolstering Britain's economy with his business-friendly policies, and Disraeli prevented the working-class from falling to socialism with his One-Nation Conservatism. Salisbury was one of our greatest but overlooked Prime Ministers, expanding the empire in Africa and presiding over the height of Britain's imperial preeminence.
Napoleon was terrible at chess, there's even an awful opening named after him.