Emperor of the French (1852-1870). A nephew of Napoleon I, he led the opposition to Louis Philippe and became president of the Second Republic (1848-1852). After proclaiming himself emperor (1852), he instituted reforms and rebuilt Paris. His successful imperialist ventures were overshadowed by a failed campaign in Mexico (1861-1867) and the Franco-Prussian War (1870-1871), which resulted in his deposition.