Question: Who is the paternal grandfather of Władysław I Of Płock?

Knowledge 1: 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. [SEP] Knowledge 2: 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 brotherJanuszI 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.
Knowledge 1: 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. [SEP] Knowledge 2: 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.
Knowledge 1: 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. [SEP] Knowledge 2: 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.

Answer: Siemowit III, Duke of Masovia