Casimir I of Kuyavia

Casimir I of Kuyavia (c. 1211–1267) was a Piast prince, second son of Konrad I of Masovia. He received Kuyavia from his father in 1233 and Ląd on his marriage to Constance, and after Konrad's death in 1247 seized Sieradz-Łęczyca and Dobrzyń from his brothers. His bid to Christianize the Yotvingians failed amid Teutonic opposition, so he settled Templars at Łuków.

A coalition led by Bolesław the Pious forced him to cede Ląd in 1261. His third wife, Euphrosyne of Opole, bore Władysław I the Elbow-high, the future king of reunited Poland. Casimir died in 1267.