Catherine II (Russian: Екатерина II Великая, Yekaterina II Velikaya), also known as Catherine the Great, born 2 May [O.S. 21 April] 1729, reigned as Empress of Russia from 9 July [O.S. 28 June] 1762 until her death (17 November [O.S. 6 November] 1796). Under her direct auspices the Russian Empire expanded, improved its administration, and continued to modernize along Western European lines. Catherine's rule re-vitalized Russia, which grew ever stronger and became recognized as one of the great powers of Europe. Her successes in complex foreign policy and her sometimes brutal reprisals in the wake of rebellion (most notably Pugachev's Rebellion) complemented her hectic private life. She frequently occasioned scandal — given her propensity for lascivious relationships which often resulted in gossip flourishing within more than one European court. This gossip is seen today by many as true, but historians believe that almost all of these accusations are false.

Catherine took power after a conspiracy deposed her husband, Peter III (1728–1762), and her reign saw the high point in the influence of the Russian nobility. Peter III, under pressure from the nobility, had already increased the authority of the great landed proprietors over their muzhiks and serfs. In spite of the duties imposed on the nobles by the first prominent "modernizer" of Russia, Tsar Peter I (1672–1725), and despite Catherine's friendships with the western European thinkers of the Enlightenment (in particular Denis Diderot, Voltaire and Montesquieu) Catherine found it impractical to improve the lot of her poorest subjects, who continued to suffer, e.g., military conscription. The distinctions between peasant rights on votchina and pomestie estates virtually disappeared in law as well as in practice during her reign.

In 1775 Catherine decreed a Statute for the Administration of the Provinces of the Russian Empire. The Statute sought to efficiently govern Russia by increasing population and dividing the country into provinces and districts. By the end of her reign, there were fifty provinces, nearly 500 districts, more than double the government officials, and they were spending six times as much as previously on local government. In 1785 Catherine conferred on the nobility the Charter to the Nobility, increasing further the power of the landed oligarchs. Nobles in each district elected a Marshal of the Nobility who spoke on their behalf to the monarch on issues of concern to them — mainly economic ones. In the same year, Catherine issued the Charter of the Towns which distributed all people into six groups in order to control the power of nobles and create a middle estate. Each of these charters had major flaws and Catherine seemingly could not gain the reform she had long desired for her country, after her death this was made even more obvious through her son Paul.

Catherine's father Christian August, Prince of Anhalt-Zerbst belonged to the ruling family of Anhalt, but entered the service of Prussia and held the rank of a Prussian general in his capacity as Governor of the city of Stettin (now Szczecin, Poland) in the name of the king of Prussia. Born as Sophia Augusta Frederica (German: Sophie Friederike Auguste von Anhalt-Zerbst-Dornburg, nicknamed "Figchen") in Stettin, Pomerania, Catherine did have some (very remote) Russian ancestry, and two of her first cousins became Kings of Sweden: Gustav III and Charles XIII. In accordance with the custom then prevailing in the ruling dynasties of Germany, she received her education chiefly from a French governess and from tutors.

The choice of Sophia as wife of her second cousin, the prospective tsar – Peter of Holstein-Gottorp – resulted from some amount of diplomatic management in which Count Lestocq, Peter's aunt (the ruling Russian Empress Elizabeth) and Frederick II of Prussia took part. Lestocq and Frederick wanted to strengthen the friendship between Prussia and Russia in order to weaken the influence of Austria and to ruin the Russian chancellor Bestuzhev, on whom Tsarina Elizabeth relied, and who acted as a known partisan of Russo-Austrian co-operation. The diplomatic intrigue failed, largely due to the intervention of Sophie's mother, Johanna Elisabeth of Holstein-Gottorp, a clever and ambitious woman. Historical accounts portray Catherine's mother as an emotionally cold and physically abusive woman who loved gossip and court intrigues. Johanna's hunger for fame centered on her daughter's prospects of becoming empress of Russia, but she infuriated Empress Elizabeth, who eventually banned her from the country for spying for King Frederick of Prussia. The empress knew the family well: she herself had intended to marry Princess Johanna's brother Charles Augustus (Karl August von Holstein), who had died of smallpox in 1727 before the wedding could take place. Nonetheless, Elizabeth took a strong liking to the daughter, who on arrival in Russia spared no effort to ingratiate herself not only with the Empress Elizabeth, but with her husband and with the Russian people. She applied herself to learning the Russian language with such zeal that she rose at night and walked about her bedroom barefoot repeating her lessons (though she mastered the language, she retained an accent). This resulted in a severe attack of pneumonia in March 1744. When she wrote her memoirs she represented herself as having made up her mind when she came to Russia to do whatever seemed necessary, and to profess to believe whatever required of her, in order to become qualified to wear the crown. The consistency of her character throughout life makes it highly probable that even at the age of fifteen she possessed sufficient maturity to adopt this worldly-wise line of conduct.

Princess Sophia's father, a very devout Lutheran, strongly opposed his daughter's conversion to Eastern Orthodoxy. Despite his instructions, on 28 June 1744 the Russian Orthodox Church received Princess Sophia as a member with the "new" name Catherine (Yekaterina or Ekaterina) and the (artificial) patronymic Алексеевна (Alekseyevna, daughter of Aleksey). On the following day the formal betrothal took place. The long-planned dynastic marriage finally occurred on 21 August 1745 at Saint Petersburg. Sophia had reached the age of 16; her father did not travel to Russia for her wedding. The bridegroom, known then as Peter von Holstein-Gottorp, had become Duke of Holstein-Gottorp (located in the north-west of present-day Germany near the border with Denmark) in 1739. The newlyweds settled in the palace of Oranienbaum, which would remain the residence of the "young court" for many years to come.

Count Andrei Shuvalov, chamberlain to Catherine, knew the diarist James Boswell well, and Boswell reports that Shuvalov shared private information regarding the monarch's intimate affairs. Some of these rumours included that Peter took a mistress (Elizabeth Vorontsova), while Catherine carried on liaisons with Sergei Saltykov, Grigory Grigoryevich Orlov (1734–1783), Stanisław August Poniatowski, Alexander Vassilchikov, and others. She became friends with Princess Ekaterina Vorontsova-Dashkova, the sister of her husband's mistress, who introduced her to several powerful political groups which opposed her husband. Catherine read extensively and kept up-to-date on current events in Russia and in the rest of Europe. She corresponded with many of the prominent minds of her era, including Voltaire and Denis Diderot.

After the death of the Empress Elizabeth on 5 January 1762 [O.S. 25 December 1761], Peter, the Grand Duke of Holstein-Gottorp, succeeded to the throne as Peter III of Russia, and his wife, Grand Duchess Catherine became Empress Consort of Russia. The imperial couple moved into the new Winter Palace in Saint Petersburg. The new tsar's eccentricities and policies, including a great admiration for the Prussian king, Frederick II alienated the same groups that Catherine had cultivated. Besides, Peter intervened in a dispute between his Duchy of Holstein and Denmark over the province of Schleswig. Peter's insistence on supporting Frederick II of Prussia, who had seen Berlin occupied by Russian troops in 1760 but now suggested partitioning the Polish territories with Russia, eroded much of his support among the nobility. (Russia and Prussia fought each other during the Seven Years War (1756–1763) until Peter's accession.) In July 1762, barely six months after becoming the Tsar, Peter committed the political error of retiring with his Holstein-born courtiers and relatives to Oranienbaum, leaving his wife in Saint Petersburg. On 13 July and 14 July the Leib Guard revolted, deposed Peter, and proclaimed Catherine the ruler of Russia. The bloodless coup succeeded. But three days after the coup, on 17 July 1762 – just six months after his accession to the throne – Peter III died at Ropsha, at the hands of Alexei Orlov (younger brother to Gregory Orlov, then a court favorite and a participant in the coup). Historians find no evidence for Catherine's complicity in the supposed assassination. (Note that at that time other potential rival claimants to the throne existed: Ivan VI (1740–1764), in closed confinement at Schlüsselburg, in Lake Ladoga, from the age of 6 months; and Princess Tarakanova (1753–1775).)

Catherine, although not descended from any previous Russian emperor, succeeded her husband as Empress Regnant. She followed the precedent established when Catherine I (born in the lower classes in the Swedish East Baltic territories) succeeded her husband Peter I in 1725. Legitimists debate Catherine's technical status: seeing her as a Regent or as a usurper, tolerable only during the minority of her son, Grand Duke Paul. In the 1770s a group of nobles connected with Paul (Nikita Panin and others) contemplated the possibility of a new coup to depose Catherine and transfer the crown to Paul, whose power they envisaged restricting in a kind of constitutional monarchy. However, nothing came of this, and Catherine reigned until her death.

During her reign Catherine extended the borders of the Russian Empire southward and westward to absorb New Russia, Crimea, Right-Bank Ukraine, Belarus, Lithuania, and Courland at the expense, mainly, of two powers – the Ottoman Empire and the Polish–Lithuanian Commonwealth. All told, she added some 200,000 miles² (518,000 km²) to Russian territory. Catherine's foreign minister, Nikita Panin (in office 1763–1781), exercised considerable influence from the beginning of her reign. A shrewd statesman, Panin dedicated much effort and millions of rubles to setting up a "Northern Accord" between Russia, Prussia, Poland, and Sweden, to counter the power of the Bourbon–Habsburg League. When it became apparent that his plan could not succeed, Panin fell out of favor and Catherine had him replaced with Ivan Osterman (in office 1783–1797). Catherine agreed a commercial treaty with Great Britain in 1766, but stopped short of a full military alliance. Although she could see the benefits of Britain's friendship, she was wary of Britain's increased power following their victory in the Seven Years War which threatened the European Balance of Power.

While Peter the Great had succeeded only in gaining a toehold in the south on the edge of the Black Sea in the Azov campaigns, Catherine completed the conquest of the south that Peter had begun. Catherine made Russia the dominant power in south-eastern Europe after her first Russo-Turkish War against the Ottoman Empire (1768–1774), which saw some of the heaviest defeats in Turkish history, including the Battle of Chesma (5–7 July 1770) and the Battle of Kagul (21 July 1770). The Russian victories allowed Catherine's government to obtain access to the Black Sea and to incorporate the vast steppes of present-day southern Ukraine, where the Russians founded the new cities of Odessa, Nikolayev, Yekaterinoslav (literally: "the Glory of Catherine"; the future Dnepropetrovsk), and Kherson. Catherine annexed the Crimea as late as 1783, a mere nine years after the Crimean Khanate had gained independence, guaranteed by Russia, from the Ottoman Empire as a result of her first war against the Turks. The palace of the Crimean khans passed into the hands of the Russians. The Treaty of Kutschuk Kainardzhi, signed 10 July 1774, gave to the Russians the "new" territories at Azov, Kerch, Yenikale, Kinburn and the small strip of Black Sea coast between the rivers Dnieper and Bug. The Ottomans re-started hostilities in the second Russo-Turkish War (1787–1792). This war proved catastrophic for the Ottomans and ended with the Treaty of Jassy (1792), which legitimized the Russian claim to the Crimea.

Ever conscious of her legacy, Catherine longed for recognition as an enlightened sovereign. She pioneered for Russia the role that Britain would later play throughout most of the nineteenth and early twentieth century  – that of international mediator in disputes that could, or did, lead to war. Accordingly, she acted as mediator in the War of the Bavarian Succession (1778–1779) between Prussia and Austria. In 1780 she set up a League of Armed Neutrality designed to defend neutral shipping from the British Royal Navy during the American Revolution.

From 1788 to 1790, Russia fought in the Russo-Swedish War against Sweden, instigated by Catherine's cousin, King Gustav III of Sweden. Expecting to simply overtake the Russian armies still engaged in war against the Ottoman Turks and hoping to strike Saint Petersburg directly, the Swedes ultimately faced mounting human and territorial losses when opposed by Russia's Baltic Fleet. After Denmark declared war on Sweden in 1788 (the Theater War), things looked bleak for the Swedes. After the Battle of Svensksund in 1790, the parties signed the Treaty of Värälä (14 August 1790) returning all conquered territories to their respective owners, and peace ensued for 20 years, aided by the assassination of Gustav III in 1792.

In 1764 Catherine placed Stanisław Poniatowski, her former lover, on the Polish throne. Although the idea of partitioning Poland came from the Prussian king Frederick the Great, Catherine took a leading role in carrying this out in the 1790s. In 1768 she formally became protectress of the Polish–Lithuanian Commonwealth, an event which provoked an anti-Russian uprising in Poland, the Confederation of Bar (1768–1772). After smashing the uprising she established in the Rzeczpospolita a system of government fully controlled by the Russian Empire through a Permanent Council under the supervision of her ambassadors and envoys. After the French Revolution of 1789, Catherine rejected many of the principles of the Enlightenment which she had once viewed favorably. Afraid that the May Constitution of Poland (1791) might lead to a resurgence in the power of the Polish–Lithuanian Commonwealth and that the growing democratic movements inside the Commonwealth might become a threat to the European monarchies, Catherine decided to intervene in Poland. She provided support to a Polish anti-reform group known as the Targowica Confederation. After defeating Polish loyalist forces in the Polish War in Defense of the Constitution (1792) and in the Kościuszko Uprising (1794), Russia completed the partitioning of Poland, dividing all of the remaining Commonwealth territory with Prussia and Austria (1795).

In the Far East, Russians became active in fur-trapping in Kamchatka and in the Kuril Islands. This spurred Russian interest in opening trade with Japan to the south for supplies and food. In 1783 storms drove a Japanese sea-captain, Daikokuya Kōdayū, ashore in the Aleutian Islands, at that time Russian territory. Russian local authorities helped his party, and the Russian government decided to use him as a trade envoy. On 28 June 1791, Catherine granted Kōdayū an audience at Tsarskoye Selo. Subsequently, in 1792, the Russian government dispatched a trade-mission led by Adam Laxman to Japan. The Tokugawa government received the mission, but negotiations failed.

Catherine's patronage furthered the evolution of the arts in Russia more than that of any Russian sovereign before or after her.
Catherine had a reputation as a patron of the arts, literature and education. The Hermitage Museum, which now occupies the whole of the Winter Palace, began as Catherine's personal collection. At the instigation of her factotum, Ivan Betskoi, she wrote a manual for the education of young children, drawing from the ideas of John Locke, and founded (1764) the famous Smolny Institute, admitting young girls of the nobility. She wrote comedies, fiction and memoirs, while cultivating Voltaire, Diderot and d'Alembert – all French encyclopedists who later cemented her reputation in their writings. The leading economists of her day, such as Arthur Young and Jacques Necker, became foreign members of the Free Economic Society, established on her suggestion in Saint Petersburg in 1765. She lured the scientists Leonhard Euler and Peter Simon Pallas from Berlin to the Russian capital. Catherine enlisted Voltaire to her cause, and corresponded with him for 15 years, from her accession to his death in 1778. He lauded her accomplishments, calling her "The Star of the North" and the "Semiramis of Russia" (in reference to the legendary Queen of Babylon, a subject on which he published a tragedy in 1768). Though she never met him face-to-face, she mourned him bitterly when he died, acquired his collection of books from his heirs, and placed them in the National Library of Russia. Within a few months of her accession in 1762, having heard that the French government threatened to stop the publication of the famous French Encyclopédie on account of its irreligious spirit, Catherine proposed to Diderot that he should complete his great work in Russia under her protection.

Four years later, 1766, she endeavoured to embody in a legislative form the principles of Enlightenment which she had imbibed from the study of the French philosophers. She called together at Moscow a Grand Commission – almost a consultative parliament – composed of 652 members of all classes (officials, nobles, burghers and peasants) and of various nationalities. The Commission had to consider the needs of the Russian Empire and the means of satisfying them. The Empress herself prepared the "Instructions for the Guidance of the Assembly", pillaging (as she frankly admitted) the philosophers of Western Europe, especially Montesquieu and Cesare Beccaria. As many of the democratic principles frightened her more moderate and experienced advisers, she refrained from immediately putting them into execution. After holding more than 200 sittings the so-called Commission dissolved without getting beyond the realm of theory. In spite of this, some later codes (such as the Statute of Local Administration 1775, the Code of Commercial Navigation and the Salt Trade Code of 1781, the Police Ordnance of 1782, the Charter to the Nobility and the Charter of the Towns of 1785, the Statute of National education of 1786) addressed some of the modernization trends implicit in Catherine's initial 1766 Nakaz. In 1777 the Empress described to Voltaire her legal innovations within an apathetic Russia as progressing "little by little". During Catherine's reign, Russians imported and studied the classical and European influences which inspired the Russian Enlightenment. Gavrila Derzhavin, Denis Fonvizin and Ippolit Bogdanovich laid the groundwork for the great writers of the nineteenth century, especially for Alexander Pushkin. Catherine became a great patron of Russian opera.

When Alexander Radishchev published his Journey from Saint Petersburg to Moscow in 1790 (one year after the start of the French Revolution) and warned of uprisings because of the deplorable social conditions of the peasants held as serfs, Catherine exiled him to Siberia. (The same sort of censorship also happened at that time in many other European countries as a reaction to the civil violence in France.) Catherine's apparent whole-hearted adoption of things Russian (including Orthodoxy) may have prompted her personal indifference to religion. She did not allow dissenters to build chapels, and she suppressed religious dissent after the onset of the French Revolution. Politically, Catherine exploited Christianity in her anti-Ottoman policy, promoting the protection and fostering of Christians under Turkish rule. She placed strictures on Roman Catholics (ukaz of 23 February 1769), mainly Polish, and attempted to assert and extend state control over them in the wake of the partitions of Poland. Nevertheless, Catherine's Russia provided an asylum and a base for re-grouping to the Society of Jesus following the suppression of the Jesuits in most of Europe in 1773.

Catherine, throughout her long reign, took many lovers, often elevating them to high positions for as long as they held her interest, and then pensioning them off with large estates and gifts of serfs. After her affair with her lover and capable adviser Grigori Alexandrovich Potemkin ended in 1776, he would allegedly select a candidate-lover for her who had both the physical beauty as well as the mental faculties to hold Catherine's interest (such as Alexander Dmitriev-Mamonov). Some of these men loved her in return, and she always showed generosity towards her lovers, even after the end of an affair. One of her lovers, Zavadovsky, received 50,000 rubles, a pension of 5,000 rubles, and 4,000 peasants in the Ukraine after she dismissed him. The last of her lovers, Prince Zubov, 40 years her junior, proved the most capricious and extravagant of them all. In her memoirs, Catherine indicated that her first lover, Sergei Saltykov, had fathered Paul, but Paul physically resembled her husband, Peter. Catherine kept near Tula, away from her court, her illegitimate son by Grigori Orlov, Alexis Bobrinskoy (later created Count Bobrinskoy by Paul).

Sir Charles Hanbury Williams, the British ambassador to Russia, offered Stanisław Poniatowski a place in the embassy in return for gaining Catherine as an ally. Poniatowski, through his mother's side, came from the Czartoryski family, prominent members of the pro-Russian faction in Poland. Catherine, 26 years old and already married to the then Grand Duke Peter for some 10 years, met the dashing 22-year-old Poniatowski in 1755, therefore well before encountering the Orlov brothers. Two years later, in 1757, Poniatowski served in the British forces during the Seven Years' War, thus severing close relationships with Catherine. She bore him a daughter named Anna Petrovna in December 1757 (not to be confused with Grand Duchess Anna Petrovna of Russia, the daughter of Peter I's second marriage).

King August III of Poland died in 1763, and therefore Poland needed to elect a new ruler. Catherine supported Poniatowski as a candidate to become the next king. Some people venture that Catherine told her ambassador to Poland, Count Kayserling, that she wanted Poniatowski to rule, but she would settle for Adam Czartoryski, Poniatowski's uncle. Catherine sent the Russian army into Poland to avoid possible disputes right away. Russia invaded Poland on 26 August 1764, threatening to fight and forcing Poniatowski to become king. Poniatowski accepted the throne, and thereby put himself under Catherine's control. News of Catherine's plan spread and Frederick II (others say the Ottoman sultan) warned her that if she tried to conquer Poland by marrying Poniatowski, all of Europe would oppose her strongly. She had no intention of marrying him, having already given birth to Orlov´s child and to the Grand Duke Paul by then; and she told Poniatowski to marry someone else, in order to remove all suspicion. Poniatowski refused: he never married.

Prussia (through the agency of Prince Henry), Russia (under Catherine), and Austria (under Maria Theresa) began preparing the ground for the Partitions of Poland. In the first partition, 1772, the three powers split 20,000 square miles (52,000 km²) between them. Russia got territories east of the line connecting, more or less, Riga–Polotsk–Mogilev. In the second partition, 1793, Russia received the most land, from west of Minsk almost to Kiev and down the river Dnieper leaving some spaces of steppe down south in front of Ochakov, on the Black Sea. After this, uprisings in Poland led to the third partition, 1795, one year before the death of Catherine.

Grigory Orlov, the grandson of a rebel in the Streltsy Uprising (1698) against Peter the Great, distinguished himself in the Battle of Zorndorf (25 August 1758), receiving three wounds. He represented an opposite to Peter's pro-Prussian sentiment, with which Catherine disagreed. By 1759, he and Catherine had become lovers although no one in the know told Catherine's husband, the Grand Duke Peter. Catherine saw Orlov as very useful, and he became instrumental in the July 1761 coup d’état against her husband, but she preferred to remain the Dowager Empress of Russia, rather than marrying anyone. Grigory Orlov and his other three brothers found themselves rewarded with titles as Counts, money, swords and other gifts. But Catherine did not marry Grigory, who proved inept at politics and useless when asked for advice. He received a palace in St. Petersburg when Catherine became Empress. Orlov died in 1783. His and Catherine's son, Aleksey Grygoriovich Bobrinsky, (1762–1813) had one daughter, Maria Alexeeva Bobrinsky (Bobrinskaya), (1798–1835) who married aged 21 in 1819 the 34-year-old Prince Nikolai Sergeevich Gagarin (London, England, 12 July 1784 – 25 July 1842, assassinated by a furious servant he employed) who took part in the Battle of Borodino ( 7 September 1812) against the Napoleonic forces, and later served as Ambassador in Turin, the capital of the Duchy of Savoy.

Grigory Potemkin had had involvement in the coup d'état of 1762. In 1772, Catherine's close friends informed her of Orlov's affairs with other women, and she dismissed him. By the winter of 1773 the Pugachev revolt had started to grow threatening. Catherine's son Paul had also started gaining support; both of these trends threatened her power. She called Potemkin for help  – mostly military  – and he became devoted to her. In 1772, Catherine wrote to Potemkin. Days earlier, she had found out about an uprising in the Volga region. She appointed General Aleksandr Bibikov to put down the uprising, but she needed Potemkin's advice on military strategy. Potemkin quickly gained positions and awards. Russian poets wrote about his virtues, the court praised him, foreign ambassadors fought for his favor, and his family moved into the palace. He later became governor of New Russia. In 1780 the son of Empress Maria Theresa of Austria, Emperor Joseph II of Austria, toyed with the idea of determining whether or not to enter an alliance with Russia, and asked to meet Catherine. Potemkin had the task of briefing him and traveling with him to Saint Petersburg. Potemkin also convinced Catherine to expand the universities in Russia to increase the number of scientists. Potemkin fell very ill in August 1783. Catherine worried that he would not finish his work developing the south as he had planned. Potemkin died at the age of fifty-two in 1791.

Catherine suffered a stroke on 6 November [O.S. 5 November] 1796 and died in her bed at 9:20 the following evening without having regained consciousness. Despite an urban myth connecting her death with a sexual incident involving a horse, there is no basis to this story. Catherine was buried at the Peter and Paul Cathedral in Saint Petersburg.