peasant woman of Baltic (probably Lithuanian) birth who became the second wife of Peter I the Great (reigned 1682–1725) and empress of Russia (1725–27).

Orphaned at the age of three, Marta Skowronska was raised by a Lutheran pastor in Marienburg (modern Alūksne, Latvia). When the Russians seized Marienburg (1702) during the Great Northern War, Marta was taken prisoner. She later was handed over to a close adviser of Peter I. A short time later she and the tsar became lovers.

In 1703, after the birth of their first child, she was received into the Russian Orthodox church and rechristened Catherine (Yekaterina) Alekseyevna. Subsequently, she became Peter's inseparable companion, and, in February 1712, his wife. On May 18 (May 7), 1724, she was crowned empress-consort of Russia.

When Peter died (Feb. 8 【Jan. 28】, 1725) without naming an heir, Catherine's candidacy for the throne was supported by the guards and by several powerful and important individuals. As a result, the Holy Synod, the Senate, and the high officials of the land almost immediately proclaimed Catherine empress of Russia. In February 1726, however, she created the Supreme Privy Council, named six of Peter's former advisers as its members, and effectively transferred control of government affairs to it, thereby undermining the authority of the Senate and the Synod, which had been Peter's main administrative instruments.

Shortly before her death, Catherine appointed Peter's grandson Pyotr Alekseyevich (reigned as Peter II; 1727–30) as her heir. Later, her daughter Elizabeth (reigned 1741–62) and her grandson Pyotr Fyodorovich (reigned as Peter III; 1762) became Russia's sovereigns.