After George Frederick's death in 1603, the Polish king Sigismund III Vasa appointed Joachim Frederick as regent in 1605, and permitted his son, John Sigismund, to succeed him in 1611.
Albert Frederick and Marie were parents to seven children: At his death, the duchy passed to his son-in-law John Sigismund, Margrave of Brandenburg, combining the two territories under a single dynasty and forming Brandenburg-Prussia.
He was a younger son of Stephen Báthory of Somlyó. Christopher's career began during the reign of Queen Isabella Jagiellon, who administered the eastern territories of the Kingdom of Hungary on behalf of her son, John Sigismund Zápolya, from 1556 to 1559.
He was one of the commanders of John Sigismund's army in the early 1560s.
Christopher's brother, Stephen Báthory, who succeeded John Sigismund in 1571, made Christopher captain of Várad (now Oradea in Romania).
At the time, Isabella administered the eastern territories of the Kingdom of Hungary on behalf of her son, John Sigismund Zápolya.
John Sigismund took charge of the administration of his realm after his mother died on 15 November 1559.
After the rebellion of Melchior Balassa, Christopher persuaded John Sigismund to fight for his realm instead of fleeing to Poland in 1562.
Christopher was one of the commanders of John Sigismund's troops during the ensuing war against the Habsburg rulers of the western territories of the Kingdom of Hungary, Ferdinand and Maximilian, who tried to reunite the kingdom under their rule.
After the death of John Sigismund, the Diet of Transylvania elected Christopher's younger brother, Stephen Báthory, voivode (or ruler) on 25 May 1571.
Born in Cölln on the Spree (today part of Berlin), George William was the son of John Sigismund, Margrave of Brandenburg and Anna of Prussia.
Joachim Frederick was succeeded at his death by his son John Sigismund.
John Sigismund (German: Johann Sigismund;
John Sigismund was born in Halle an der Saale to Joachim III Frederick, Elector of Brandenburg, and his first wife Catherine of Brandenburg-Küstrin.
In 1611, John Sigismund traveled from Königsberg to Warsaw, where on 16 November 1611 he gave feudal homage to Sigismund III Vasa, King of Poland (the Duchy of Prussia was a Polish fief at the time).
John Sigismund gave the Reichshof Castrop to his teacher and educator Carl Friedrich von Bordelius, whereas he received the territories of Cleves, Mark, and Ravensberg in the Treaty of Xanten in 1614.
John Sigismund's most significant action was his conversion from Lutheranism to Calvinism, after he had earlier equalized the rights of Catholics and Protestants in the Duchy of Prussia under pressure from the King of Poland.
Resistance was so strong that in 1615, John Sigismund backed down and relinquished all attempts at forcible conversion.
On 30 October 1594, John Sigismund married Anna of Prussia, daughter of Albert Frederick, Duke of Prussia (1553–1618).
She was a daughter of John Sigismund, Elector of Brandenburg, and Anna, Duchess of Prussia, daughter of Albert Frederick, Duke of Prussia.