This king to which Marcin Kromer was a personal secretary was also a grand duke of what country?
Marcin Kromer:  He was a personal secretary to two Kings of Poland, Sigismund I the Old and Sigismund II Augustus. Sigismund I the Old: Sigismund I of Poland (Polish: "Zygmunt I Stary" , Lithuanian: "Žygimantas I Senasis" ; 1 January 1467 – 1 April 1548), of the Jagiellon dynasty, reigned as King of Poland and also as the Grand Duke of Lithuania from 1506 until 1548.
Lithuania