Mieszko I (myĕsh´kô) or Mieczyslaw I (–chĬsläf), c.922–992, duke of Poland (962–92), the first important member of the Piast dynasty. The first German invasions of Poland began in 963. To avert this threat, Mieszko obtained (c.963) a friendly treaty with Holy Roman Emperor Otto I, to whom he agreed to pay tribute. Mieszko later conquered Pomerania. In 966 he accepted Christianity and immediately began the conversion of Poland. Late in his reign he placed Poland under the protection of the pope, thus gaining papal support of Polish integrity. His son Boleslaus I succeeded him.