Catherine II (born Sophie of Anhalt-Zerbst; 2 May 1729 – 17 November 1796), most commonly known as Catherine the Great, was the last reigning Empress Regnant of Russia (from 1762 until 1796) and the country’s longest-ruling female leader. She came to power following the overthrow of her husband and second cousin, Peter III. Under her reign, Russia grew larger, its culture was revitalized, and it was recognised as one of the great powers of Europe.

In her accession to power and her rule of the empire, Catherine often relied on her noble favourites, most notably Count Grigory Orlov and Grigory Potemkin. Assisted by highly successful generals such as Alexander Suvorov and Pyotr Rumyantsev, and admirals such as Samuel Greig and Fyodor Ushakov, she governed at a time when the Russian Empire was expanding rapidly by conquest and diplomacy. In the south, the Crimean Khanate was crushed following victories over the Bar confederation and Ottoman Empire in the Russo-Turkish War, 1768–1774. With the support of the United Kingdom, Russia colonised the territories of Novorossiya along the coasts of the Black and Azov Seas. In the west, the Polish–Lithuanian Commonwealth, ruled by Catherine's former lover King Stanislaus Augustus Poniatowski, was eventually partitioned, with the Russian Empire gaining the largest share. In the east, Russians became the first Europeans to colonise Alaska, establishing Russian America.

Catherine reformed the administration of Russian guberniyas (governorates), and many new cities and towns were founded on her orders, most notably Odessa, Dnipro, Kherson, Mykolaiv and Sevastopol. An admirer of Peter the Great, Catherine continued to modernise Russia along Western European lines. However, military conscription and the economy continued to depend on serfdom, and the increasing demands of the state and of private landowners intensified the exploitation of serf labour. This was one of the chief reasons behind rebellions, including the large-scale Pugachev Rebellion of Cossacks, nomads, peoples of Volga and peasants.

The period of Catherine the Great's rule is also known as the Catherinian Era. The Manifesto on Freedom of the Nobility, issued during the short reign of Peter III and confirmed by Catherine, freed Russian nobles from compulsory military or state service. Construction of many mansions of the nobility, in the classical style endorsed by the empress, changed the face of the country. She enthusiastically supported the ideals of the Enlightenment and is often included in the ranks of the enlightened despots. As a patron of the arts, she presided over the age of the Russian Enlightenment, including the establishment of the Smolny Institute of Noble Maidens, the first state-financed higher education institution for women in Europe.