The South Bohemian magnate, William of Rosenberg, was convinced that the history of his family reached back to Roman times and that his roots could be found in the Italian house of Orsini. This is why he started to use a different symbol from that of his ancestors. His coat of arms, which was also adopted by his brother Peter Vok, looks as follows: a shield divided by a golden bar and sometimes containing a small black snake or eel. A cinquefoil red rose is in the upper silver field and three slanted red stripes are painted in the lower silver field. The whole shield is held by two bears reminiscent of the Latin root of the name Orsini (Orsini = ursus, i.e., bear).
William of Rosenberg was born on 10th March 1535 in Upper Austrian Schützendorf. His mother was then living there with her relatives. He was the fourth child of Jošt III of Rosenberg and Anne of Rogendorf. He and his siblings (Anne, Elisabeth, Bohunka, Eve, and Peter Vok) lost their father on 15th October 1539. Discord between his mother and the new Rosenberg ruler Peter the Lame (the younger brother of Jošt III) meant that the children did not enjoyed much peace at home. During the time of his mother's forced temporary stay in Upper Austria (1542-1546), William's siblings lived in Jindřichův Hradec, with their aunt, Anne of Rosenberg, who had been born in Hradec and was the widow of Henry VII of Rosenberg.
In 1542, William stayed in the private college of Ernest Krajíř of Krajek in Mladá Boleslav for several months. Two years later, he left for Passau, where between 1544 and 1550, he attended school at the court of the local bishop, Wolfgang of Salm, a relative on his mother's side,. It could be said that those were William's only studies on the level of a contemporary high school. From 1550 onward, he continued his studies at the imperial court in Augsburg.
The motto of his life was "Festina lente", i.e., "Easy does it". Still he had to enter adult life quite quickly. When he was 16 he took control of the family wealth and became the head of his family as the "Ruler of the house of Rosenberg". Along with this title, he took over the administration of the dominions of Český Krumlov, Třeboň, Rosenberg, Nové Hrady, Helfenburg, Choustník, Miličín, Želeč, and Drslavice, the monasteries in Vyšší Brod, Zlatá Koruna, Třeboň, and Borovany, the monastery of Minorites and the convent of the Poor Clares in Český Krumlov, the parsonage in Český Krumlov, and Haslach in Upper Austria. According to Václav Březina, there were then more than 11 thousand of "the settled", i.e. homestead keepers, in the entire dominion of the Rosenbergs. That was a lot.
However, the beginning of his public activity was quite modest. In 1560, he became only the highest chamberlain, and not until 1570 did he become the highest burgrave. He accepted this position in accordance with the wish as of King Maximilian II and the Bohemian Commune of Estates. This office made him the head of a team of the highest provincial officials in the Bohemian kingdom, and it is known that William was considered the vice-king by both domestic and foreign politicians. So his role was very important, especially in light of the frequent and long-lasting absences of the Bohemian king from the country. Apart from William's ancestry, his diplomatic prudence and other positive personal qualities, a certain religious tolerance of the native Catholics towards the various Protestant streams in the Bohemian kingdom perhaps also played a role in his appointment to this office.
William of Rosenberg worked his way up among the leading diplomats of the kingdom very soon. The monarch sent him to Poland as the head of a deputation that should claim the vacant Polish throne for King Maximillian or for his son Ernest. William did not manage to get the throne for the Habsburgs, but he earned a good reputation for himself with the Polish nobility and this resulted in the throne being offered to him. He could not take it for obvious reasons, however. He was always a reasonable and cautious man, and this played a role in this instance. His philosophy of life brought him leading positions in the country for his whole life. The words of Václav Březina at the end of his manuscript of William's biography show this clearly: "To sum it up, the master was full of all virtues, sober, gentle, peaceful, brave, just and merciful, skilful, reasonable, generous but with good forethought, economic, etc."
William, however, had the lot of his own family especially at heart. His concern for its preservation led him into four sequential marriages. First, he married Catherine Brunswick (1557), second Sophia Brandenburg (1561), third Anne Mary Baden (1578), and finally Polyxena of Pernstein (1587), who outlived him. He did not live to see an heir though. He died in Prague on 31st August 1592.