Catherine I (In Russian: Екатерина I Алексеевна) (April 15, 1683/1684–May 17,1727) was the second wife of Peter the Great and Empress of Russia from 1725 until her death. With Peter, she was also co-ruler from 1724 until his death in the next year.

Catherine was born in Jakobstadt (Jekabpils), Latvia. Originally she was given the birthname of Marfa Skavronska and was the daughter of Samuil Skavronski, a Lithuanian peasant. She was married at the age of 17 to a Swedish dragoon, having been working at the time as a servant to minister Gluck of Marienburg. Russian forces captured the city, she was captured and forced to work in the laundry of the regiment which captured her.

Later she was sent to, and became the mistress of, Prince Aleksandr Menshikov, the best friend of Peter the Great. In 1703, while visiting Menshikov at his home, Peter met Marfa, and shortly after he took her as his mistress. In 1705, she converted to Orthodoxy and changed her name to Ekaterina Alexeevna. She married Peter in February of 1712 and bore him 11 children, all of whom died in childhood except for Anna and Yelizaveta.

• Grand Duchess Anna Petrovna (1708-1728)
• Empress Yelizaveta Petrovna (1709-1762
• Grand Duchess Nataliya Petrovna (1713-1715)
• Grand Duchess Margarita Petrovna (1714-1715)
• Grand Duke Pyotr Petrovich (1715-1719)
• Grand Duke Pavel Petrovich (1717-1717)
• Grand Duchess Nataliya Petrovna (1718-1725)

In 1724, Peter named her Tsaritsa and joint ruler. Peter died in early 1725 without naming a successor, encouraging the guards regiments to proclaim her as the ruler of Russia, giving her the title of Empress. The real power, however, was with her former lover, Menshikov, and the Supreme Privy Council. She was the first royal owner of the Sarskoje Selo estate, later renamed Tsarskoye Selo.