John Jagiellon

John of the Lithuanian Dukes (Jan Ochstat de Thelnicz, , ; 8 January 1499 – 18 March 1538) was Bishop of Vilnius (1519–36) and of Bishop of Poznań (1536–38). He was the bishop when Protestantism was making the first inroads into the Grand Duchy of Lithuania and took the first steps in combating it. John was an illegitimate son of Sigismund I the Old, King of Poland and Grand Duke of Lithuania, and his mistress Katarzyna Telniczanka.

Early life John was born in 1499, well before Sigismund's first marriage to Barbara Zápolya in 1512. In July 1510, John's father received papal dispensation to remove defectus natalium, recognize him as a legitimate son, and ennoble him.