Constantine Nikolayevich (kən'stəntyēn` nēkôläyā`vĭch), 1827–92, grand duke of Russia; brother of Czar Alexander II. Constantine supported all the reforms instituted by his brother, who gave him command of the fleet and made him governor-general of Poland in 1862. There his conciliatory policy could not prevent the insurrection of 1863 against Russian rule. He resigned and in 1865 was appointed president of the state council. He retired from state service in 1881.