Anna of Masovia
Anna of Masovia( c. 1498 – after 26 January 1557 in Jaroslaw) was Princess of Mazovia and a member of the House of Piast.
She was the last representative of the line of Masovian- Piast.
She was the second daughter of Konrad III of Masovia and Anna Radziwiłł.
She was a sister of Dukes Janusz III of Masovia and Stanislaus of Masovia, and Sophia, who married Stephen VII Báthory.
Siemowit III, Duke of Masovia
Siemowit III of Masovia( his name also rendered Ziemowit; – 1381) was a prince of Masovia and a co-regent( with his brother Casimir I of Warsaw) of the lands of Warsaw, Czersk, Rawa, Gostynin and other parts of Masovia.
Ladislaus of Salzburg
Władysław of Salzburg, also known as Władysław of Wrocław or Władysław of Silesia( – 27 April 1270), a member of the Silesian Piasts, was co-ruler in the Duchy of Wroclaw since 1248.
He served as chancellor of King Ottokar II of Bohemia from 1255 and was elected Bishop of Bamberg in 1257 and Bishop of Passau in 1265.
Władysław became Prince- Archbishop of Salzburg in the same year, and from 1268 also served as administrator of the Wrocław diocese.
Siemowit I of Masovia
Siemowit I of Masovia( c. 1224/28 – 23 June 1262), was a Polish prince member of the House of Piast, Duke of Czersk during 1247- 1248, Duke of Masovia( except Dobrzy ń) during 1248- 1262, ruler over Sieradz during 1259- 1260.
He was the sixth son of Konrad I of Masovia and his wife Agafia of Rus.
He was named after his older brother Siemowit, who died young in 1224.
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.
Gaudemunda of Lithuania
Gaudemunda Sophia of Lithuania( also Gaudimantė; c. 1260 – 1288/1313) was the daughter of Traidenis, Grand Duke of Lithuania( c. 1270 – 1282).
In 1279 she married Duke of Masovia Bolesław II( c. 1254–1313) of the Piast dynasty.
He was the son of Ziemowit I, Prince of Masovia, and Pereyaslava, daughter of Daniel of Galicia of the Rurik dynasty.
Her husband united the Duchy of Masovia and then divided it between their sons, who were:
Władysław I of Płock
Władysław I of Płock (pl: "
Władysław I płocki"; 1406/09 - 11/12 December 1455), was a Polish prince member of the House of Piast from the Masovian branch.
He was a Duke of Płock, Rawa Mazowiecka, Gostynin, Sochaczew, Belz, Płońsk, Zawkrze and Wizna during 1426-1434 jointly with his brothers, after the division of the paternal inheritance between him and his brothers in 1434, sole ruler over Płock, Płońsk, Wizna and Zawkrze; in 1442 he reunited all their patrimony (except Gostynin).
He was the fifth son of Siemowit IV, Duke of Masovia and Alexandra of Lithuania, daughter of Algirdas.
Jan I the Scholastic
Jan I the Scholastic( 1308 /10 – 1372 before 29 September), was a Duke of Oświęcim from 1324 until his death.
He was the eldest child and only son of Duke Władysław of Oświęcim by his wife Euphrosyne, daughter of Duke Boleslaus II of Masovia.
Siemowit IV, Duke of Masovia
Siemowit IV (Ziemowit IV), also known as Siemowit IV the Younger
(pl: "
Siemowit IV Młodszy"; ca. 1353/1356 – 21 January 1426)
, was a Polish prince member of the House of Piast from the Masovian branch, from 1373/74 Duke of Rawa, and after the division of the paternal inheritance between him and his brother in 1381, ruler over Rawa, Płock, Sochaczew, Gostynin, Płońsk and Wizna, since 1386 hereditary Polish vassal, since 1388 ruler over Belz, during 1382–1401 he lost Wizna and during 1384–1399 and 1407–1411 he lost Zawkrze, during 1384–1399 he lost Płońsk, taken by the Teutonic Order.
He was the second son of Siemowit III, Duke of Masovia and his first wife Euphemia, daughter of Nicholas II of Opava.
Already during his father's lifetime, Siemowit IV received his own district, Rawa Mazowiecka (ca. 1373/74), and as a result of the partition of Masovia between him and his older brother
Janusz
I after the death of their father on 16 June 1381, Siemowit IV finally obtain the totality of his domains:
Rawa, Płock, Sochaczew, Gostynin, Płońsk and Wizna.
Sophia of Masovia
Sophia of Masovia( 1497/1498- before 11 March 1543) was a Princess of Masovia, daughter of Konrad III Rudy, Duke of Masovia and his wife Anna Radziwiłł.
She was a member of the House of Piast.
On 17 September 1520 in Warsaw, Sophia was married by proxy to Stephen VII Báthory.
On 17 January 1521, Sophia and her entourage went to Hungary, where in February there was a formal marriage.
The couple had three children:
Anna, Stephen and Klara; however, other sources claim that Klara was the couple's only child.
Klara was engaged to Carl, Duke of Münsterberg, but died in 1535, before the marriage took place.
After the death of Stephen in 1530, Sophia was married to Croatian magnate Louis Pekry.
Sophia's second marriage was childless.
She then died sometime before 11 March 1543.
Sophia had three siblings: Stanislaus I of Masovia, Janusz III of Masovia and Anna of Masovia, both her brothers died childless and so Anna and Sophia were the last Masovian Piasts.
Soon after Janusz's death, the Duchy of Masovia was annexed into the kingdom of Poland, despite resistance from some of the Masovian nobility.
They tried to retain their independence and argued that the Duchy should be inherited by the female relatives( such as Anna or Sophia).
The Polish king refused to recognize their demands.
Anna was made titular Duchess of Masovia.

Question: What is the date of death of Władysław I Of Płock's father?
Answer: 21 January 1426