Bolesław of Kuyavia
Bolesław of Kuyavia( also known as Mieszkowic)( 1159 – 13 September 1195) was a Duke of Kuyavia from 1186 until his death.
He was the eldest child( but third- born son) of Mieszko III the Old, Duke of Greater Poland and High Duke of Poland in 1173, by his second wife Eudoxia, daughter of Grand Prince Iziaslav II of Kiev.
Casimir I of Kuyavia
Casimir I of Kuyavia  (c. 1211 – 14 December 1267), 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.
He was the second son of Konrad I of Masovia and his wife Agafia of Rus.
He was probably named after his grandfather, Casimir II the Just.
Konrad I of Masovia
Konrad I of Masovia  (ca. 1187/88 – 31 August 1247), from the Polish Piast dynasty, was the sixth Duke of Masovia and Kujawy from 1194 until his death as well as High Duke of Poland from 1229 to 1232 and again from 1241 to 1243.
Ziemomysł of Kuyavia
Ziemomysł of Inowrocław( c. 1245 – October/ 24 December 1287), was a Polish prince member of the House of Piast, Duke of Inowrocław during 1267- 1271 and 1278- 1287, and ruler over Bydgoszcz during 1267- 1269 and 1278- 1287.
He was the second son of Casimir I of Kuyavia and his second wife Constance, daughter of Henry II the Pious.
Casimir II of Łęczyca
Casimir II of Łęczyca( pl:" Kazimierz II łęczycki"; c. 1261/62 – 10 June 1294), was a Polish prince member of the House of Piast, Duke of Brześć Kujawski during 1267 – 1288, Duke of Dobrzy ń during 1275 – 1288 and Duke of Łęczyca since 1288 until his death.
He was the fourth son of Casimir I of Kuyavia, but the second born from his third marriage with Euphrosyne, daughter of Casimir I of Opole.
He was probably named after both his father and maternal grandfather.
Siemowit of Dobrzyń
Siemowit of Dobrzy ń( pl:" Siemowit dobrzyński"; c. 1262/67 – 1312), was a Polish prince member of the House of Piast, Duke of Brześć Kujawski during 1267 – 1288, Duke of Dobrzy ń during 1288 – 1293, 1295– 1303 and 1305 – 1312, during 1293 – 1295 in captivity in Lithuania, during 1303 – 1305 deposed, since 1306 hereditary vassal of the Kingdom of Poland.
He was the fifth son of Casimir I of Kuyavia, but the third born from his third marriage with Euphrosyne, daughter of Casimir I of Opole.
Adelaide of Poland
Adelaide of Poland( c. late 1170s/ early 1180s – 8 December 1211), was a Polish princess and member of the Piast dynasty.
She was the daughter of Casimir II the Just, Duke of Sandomierz and High Duke of Poland, by his wife Helena of Znojmo, a Přemyslid princess.
On basis of the inscription of her tombstone at the Dominican Church and Convent of St. James in Sandomierz and two different reports of Jan Długosz, modern historians agreed with the origin and facts from Adelaide's life.
Today existed a dominant view in historiography consistent with her filiation and death date.
According to them, Adelaide was indeed the daughter of Casimir II the Just and died in 1211, but was n't the foundress of the Convent of St. James and only another nun there.
In the 19th century, appeared a theory which states that Adelaide was the daughter of Casimir I of Kuyavia, who entered in the Convent of St. James as a nun and died there in 1291.
This view, accepted by several scholars, has been disputed.
More recent historiography recognized her as the daughter of Casimir II the Just, founder of the Convent, in which was she buried after her death in 1211.
Constance of Wrocław
Constance of Wrocław( c.1221–27 – 21 or 23 February 1257) was a Princess of Silesia and the Duchess of Kuyavia.
She was a member of the Polish House of Piast and mother of Leszek the Black and Ziemomysł of Kuyavia.
Theodred II (Bishop of Elmham)
Theodred II was a medieval Bishop of Elmham.
The date of Theodred's consecration unknown, but the date of his death was sometime between 995 and 997.
Euphemia of Kuyavia
Euphemia of Kuyavia( c. 1265 – March 18, 1308) was a Kuyavian princess, who was Queen consort of Galicia- Volhynia.
She was the daughter of Casimir I of Kuyavia by his third wife Euphrosyne, daughter of Casimir I of Opole.
Euphemia was sister of Władysław I the Elbow- high, she was wife of Yuri I of Galicia and mother of Andrew of Galicia and Lev II of Galicia.
The only preserved evidence of Euphemia's existence is from Jan Długosz's Yearbooks, which reported that on March 18, 1308 Euphemia died and that she was the daughter of Prince Casimir and the wife of Yuri I, who died in the same year on April 21, which was also his birthday.

Question: What is the date of death of Casimir I Of Kuyavia's father?
Answer: 31 August 1247