Casimir I of Kuyavia, was a Polish prince member of the House of Piast, Duke of Kujawy since 1233, ruler over Ląd during 1239-1261, ruler over Wyszogród since 1242, Duke of Sieradz during 1247-1261, Duke of Łęczyca since 1247 and Duke of Dobrzyń since 1248. Wikipedia