Peter I, also known as Peter the Great, was a Russian tsar who ruled from 1682 to 1725. He is known for his efforts to modernize Russia and bring it into the European sphere. Peter implemented a range of reforms, including military, administrative, and cultural changes, and he is credited with expanding Russia's territory and influence. He also founded the city of St. Petersburg and sought to westernize Russian society. Peter the Great is considered one of the most influential and significant rulers in Russian history.