John from the kindred Csák (; died before 1324) was a Hungarian baron at the turn of the 13th and 14th centuries. He served as Master of the horse in the 1290s. Following the extinction of the Árpád dynasty, he initially supported pretender Wenceslaus, but later joined the allegiance of Charles I. He was made Judge royal in 1311, putting end to a more than ten years of vacancy. He betrayed the King and joined his distant relative, the rebellious oligarch Matthew Csák in 1314.
Early career
John was born into the Újlak (Ilok) branch of the extended and powerful gens (clan) Csák. His father was Csák, who was mentioned by contemporary records in the period between 1240 and 1274. John had numerous illustrious close relatives, including his second cousin Ugrin Csák, the de facto ruler of Upper Syrmia in the early 14th century. John had no known descendants.
John first appeared in contemporary documents in 1295, although two non-authentic charters refer to him as Master of the horse and ispán of Baranya County in July 1290. He was considered a supporter of Andrew III, the last Hungarian monarch from the Árpád dynasty. For his court service, John was granted the castle of Visk (or Wysk) and its surrounding lands in Hont County (present-day Vyškovce nad Ipľom in Slovakia) on 25 April 1296. He served as Master of the horse in 1297, replacing his relative Matthew Csák. He is the last known person, who held the dignity during the Age of Árpáds. He functioned as ispán of Hont County in 1298. He was ispán of Baranya County in 1300. It is plausible that his latter function was highly nominal, as the county was ruled by the Kőszegi family, in addition to other parts of Transdanubia.
During the Interregnum
Andrew III died on 14 January 1301. A civil war between various claimants to the throne—Charles of Anjou, Wenceslaus of Bohemia, and Otto of Bavaria—followed Andrew's death and lasted for seven years. Initially, John supported Wenceslaus in the war of succession, despite that Ugrin Csák, also from the clan's Újlak branch, was considered the strongest domestic pillar of Charles' dominion in the early years. John was first styled as a "baron" and member of the royal court of Wenceslaus in 1303. In the same year, the young king transcribed and confirmed the letter donation of the late Andrew III, regarding the ownership of Visk.
By 1307, John Csák took an oath of allegiance to Charles of Anjou. He played an important role in the capture of Buda in June. Returning from his Bohemian captivity, the ex-rector Ladislaus, son of Werner marched into the town with the assistance of John Csák's troops. As the Illuminated Chronicle narrates, Ladislaus and John infiltrated into the fort through the gate next to the Jewish synagogue at night. Their troops clashed with the guards of the city magistrate, who refused to acknowledge Charles as their legitimate king. The pro-Wenceslaus rector Petermann escaped from the scene without clothing, while other German burghers were tortured and massacred. John captured and sent to the court of Archbishop Thomas of Esztergom those local pro-Wenceslaus clergymen, who even excommunicated Pope Boniface VIII prior to that, and were labelled as heretics. Historian Gyula Kristó analyzed the royal documents of the decade and placed John to the fifth or sixth most prominent partisan of Charles I in the subsequent years.