Elizabeth Lucretia, Duchess of Cieszyn
Elizabeth Lucretia of Cieszyn; 1 June 1599 – 19 May 1653), was a reigning Duchess of Cieszyn( Teschen, Těšín) from 1625 until her death.
Born as the third child and second daughter of Adam Wenceslaus, Duke of Cieszyn( by his wife Elisabeth, daughter of Gotthard Kettler, Duke of Courland), she was the last ruler of Cieszyn from the Polish Piast dynasty.
Jan of Cieszyn
Jan of Cieszyn( 1339/40 – after 18 May 1359), was a Polish prince, member of the Piast dynasty in the Cieszyn branch.
He was the fourth son of Casimir I, Duke of Cieszyn, by his wife Euphemia, daughter of Duke Trojden I of Czersk- Warsaw.
Siemowit of Cieszyn
Siemowit of Cieszyn( – 25 September 1391) was a Polish prince, member of the Piast dynasty in the Cieszyn branch.
He was the fifth son of Casimir I, Duke of Cieszyn, by his wife Euphemia, daughter of Duke Trojden I of Czersk- Warsaw.
Bolesław of Cieszyn (died 1356)
Bolesław of Cieszyn( – Prague, 23 July 1356), was a Polish prince, member of the Piast dynasty in the Cieszyn branch.
He was the second son of Casimir I, Duke of Cieszyn, by his wife Euphemia, daughter of Duke Trojden I of Czersk- Warsaw.
Władysław of Cieszyn (d. 1355)
Władysław of Cieszyn( 1325/31 – May 1355) was a Polish prince member of the Piast dynasty in the Cieszyn branch.
He was the eldest son of Casimir I, Duke of Cieszyn, by his wife Euphemia, daughter of Duke Trojden I of Czersk- Warsaw.
Wenceslaus II, Duke of Cieszyn
Wenceslaus II of Cieszyn( b. 1488/96- d. 17 November 1524), was a Duke of Cieszyn since 1518 until his death( as co-ruler of his father).
He was the second son of Casimir II, Duke of Cieszyn, by his wife Johanna, daughter of Wiktoryn of Poděbrady, Duke of Opawa.
Casimir I, Duke of Cieszyn
Casimir I of Cieszyn (1280/90 –), was Duke of Cieszyn from 1315, Duke of Siewierz from 1337 and Duke of Bytom from 1357.
He was the second son of Mieszko I, Duke of Cieszyn by his wife, probably called Grzymisława.
Mieszko I, Duke of Cieszyn
Mieszko I of Cieszyn (also known as Mieszko I of Opole; 1252/56 – by 27 June 1315), was a Duke of Racibórz during 1282–1290 (with his brother as co-ruler) and the first Duke of Cieszyn since 1290 until his death.
He was the oldest son of Władysław, Duke of Opole-Racibórz, by his wife Euphemia, daughter of Władysław Odonic, Duke of Greater Poland.
Bolesław IV of Legnica
Bolesław IV of Legnica( ca. 1349 – 3/4 March 1394) was a Duke of Legnica since 1364( nominally; together with his brothers).
He was the third son of Wenceslaus I, Duke of Legnica by his wife Anna, daughter of Casimir I, Duke of Cieszyn.
Elisabeth of Cieszyn
Elisabeth of Cieszyn( after 1340? – after 20 January 1364), was a Polish princess, member of the Piast dynasty in the Cieszyn branch.
She was the fourth daughter and youngest child of Casimir I, Duke of Cieszyn, by his wife Euphemia, daughter of Duke Trojden I of Czersk- Warsaw.

Question: What nationality is Casimir I, Duke Of Cieszyn's father?
Answer: Poland