Péter; c. 1240 – 1283 or 1284) was a powerful Hungarian baron, landowner and military leader, who held several secular positions during the reign of kings Stephen V and Ladislaus IV.

His son and heir was the oligarch Matthew III Csák, who, based on his father and uncles' acquisitions, became the de facto ruler of his domain independently of the king and usurped royal prerogatives on his territories.

He was born into the gens Csák as the youngest son of Matthew I, founder and first member of the Trencsén branch, who served as Master of the treasury (1242–1245), and Margaret from an unidentified noble family.

[1] Peter's elder brothers were Mark I, ispán (comes) of Hont County in 1247, but there is no further information about him; Stephen I, Master of the stewards from 1275 to 1276 and from 1276 to 1279; and Matthew II, a notable general and Palatine of Hungary (1278–1280; 1282–1283).

[3] Their son, Stephen Sternberg (or "the Bohemian") later inherited the Csák dominion because of the absence of a direct adult male descendant after the death of Matthew III in 1321.

[1] The marriage produced two children; the eldest one was Matthew III, who inherited his father and uncles' property and large-scale possessions,[5] which laid the foundation of a de facto independent domain, encompassing the north-western counties of the kingdom (today roughly the western half of present-day Slovakia and parts of Northern Hungary).

After that he successfully fought against the Cumans, who allied Béla, near the Fortress of Déva (today: Deva, Romania), where he lost a lot of soldiers, but prevented the destruction of the region.

Duke Stephen entrusted his faithful confidant Peter Csák with gathering a small contingent and marching into Northeast Hungary to rescue his family.

Peter Csák successfully recaptured the fort of Baranka (today: Bronjka, Ukraine) from Duchess Anna's troops, but his small army was unable to achieve further victories and could not prevent the permanent internment of Queen Elizabeth and the children in Béla's domain.

[15] When Stephen V ascended the throne in 1270, Peter I was appointed Master of the stewards and head of Gacka (Gecske) źupa in the Kingdom of Croatia,[16] while his elder brother, Matthew II became Voivode of Transylvania.

[19] And at the Castle of Moson, he /Peter de genere Csák/ rescued Duke Béla (our dear cousin who had been fighting to the best of his ability) from the hands of our enemies who were endeavoring to kill him cruelly with all their might.During the time when tensions emerged between Béla IV and his son, Stephen, two rival baronial groups developed, one of them was led by Henry I Kőszegi ("Henry the Great"), also involving the Gutkeled and Geregye clans, while the Trencsén branch of the Csák clan dominated the second group.

[22] Peter I regained his influence in June 1273, when he received land donations from the king, for instance Szenic in Nyitra County (today: Senica, Slovakia).

[14] The Csák brothers (Matthew II and Peter) and his allies successfully removed Joachim Gutkeled and Henry Kőszegi from power by the summer of 1274.

[1] After that the Csák clan regained the lost positions; Matthew II was appointed Voivode of Transylvania, while Peter became ispán (comes) of Somogy and Sopron Counties, which dignities held until 1275.

[25] The Csák clan had four office-holder family members during that time and they had prominent role in creating of the alliance between Ladislaus IV and Rudolf of Habsburg against Ottokar II.

Furthermore, Peter intended to gain lands and customs duties in Pozsony County, according to a charter following his death, he had taken away the letters of privilege of the nobles in Padány (today: Padáň, Slovakia) by force.