Casimir Ier d' Opole (in Polish Kazimierz I Opolski ) of the dynasty of the Piasts, was born in 1178 or 1179, and deceased the May 13rd 1230. He is the son of Mieszko IV Legs Frays and of Ludmiła of Bohemia.

He was the Duc of Opole and Racibórz of 1211 with 1230.

Casimir was born in an unstable political context, Mieszko III the Old man being isolated capacity with Cracow, his successor Casimir II the Juste, to avoid new conflicts, distributes grounds, in particular with the father of Casimir d' Opole who until there was the ally of Mieszko III the Old man.

Casimir d' Opole succeeds his father in 1211.

At the beginning, Casimir belongs to the camp of the young people Piasts (Lech Ier the White, Conrad Ier de Mazovie and Ladislas Odonic) which is opposed to the policy followed by the old ones that are Ladislas III with the Legs Hails and Henri Ier Bearded the. He grants many Privilège S to the Église, needing the support of this one in front of the appetite of his more powerful neighbors.

The Silesian threat of the duke Henri Ier the Bearded one being specified more and more, it made the only possible decision, a policy of close cooperation with its neighbor. Thus in 1225, it supports Henri Ier militarily the Bearded one when this one besieges Cracow to try to seize the throne. Alliance with Henri Ier enables him to make temporary territorial profits, as in 1227, after the assassination of Lech the White, benefitting from the free-for-all between the applicants with the throne, it annexes for one short period thestrong one of Czeladź.

Imitating Henri Ier, it as tries to attract German colonists in his duchy, with less success as in Low-Silesia. It grants the Droits of Magdeburg to several localities to support the economic development of its duchy.

It is deceased the May 13rd 1230. Henri Ier the Bearded one with taken under its protection its widow, her two sons (Mieszko and Ladislas) and his/her two daughters (Więcesława and Euphrosyne).