Historical founder of the House of Piast

Mieszko I was Duke of Poland from 960 until his death in 992 and the founder of the first unified Polish state, the Civitas Schinesghe. A member of the Piast dynasty, he was the first Christian ruler of Poland and continued the policies of both his father Siemomysł and his grandfather Lestek, who initiated a process of unification among the Polish tribes and the creation of statehood.

According to existing sources, Mieszko I was a potent politician, a talented military leader and a charismatic ruler. Through both alliances and military force, he extended ongoing Polish conquests. Early in his reign, he subjugated Kuyavia and likely Gdańsk Pomerania and Masovia. For most of his reign, Mieszko I waged war for control of Western Pomerania. He eventually annexed it to the vicinity of the lower Oder River. His internal reforms were aimed at expanding and improving the so-called war monarchy system. During the last years of his life, he fought the Bohemian state and captured Silesia and lands now constituting Lesser Poland.

In foreign policy, Mieszko I placed the interests of his country foremost and entered into agreements with his former foes. He successfully used diplomacy by concluding alliances with Bohemia, Sweden and the Holy Roman Empire. Mieszko's alliance with the Czech prince Boleslaus the Cruel was strengthened by his marriage in 965 to the Přemyslid princess Dobrawa, who is said to have brought the Christian faith to Poland. Mieszko's baptism in 966 placed him and his country in the cultural sphere of Western Christianity; he is sometimes called the "Clovis of Poland" for his role in laying the foundations for a Christian Poland. On his death, he left to his son and successor, Bolesław I the Brave, a country with greatly expanded territories and a well-established position in Europe.

Mieszko I also enigmatically appeared as "Dagome" in a papal document dating to about 1085, called Dagome iudex, which mentions a gift or dedication of Mieszko's land to the Pope almost a hundred years earlier. The term possibly refers to Mieszko's adopted Christian name, Dagobert, which often features in historical writing. Most sources also identify Mieszko I as the father of Sigrid the Haughty, a Scandinavian queen, the grandfather of Canute the Great and the great-grandfather of Gunhilda of Denmark, Canute the Great's daughter and wife of Henry III, Holy Roman Emperor.

It is roughly to his borders that Poland was returned in 1945.