He first served as ban in the service of King Peter Krešimir IV. Afterwards, Peter Krešimir IV appointed him duke and declared him as his heir. In 1075, Demetrius Zvonimir succeeded to the Croatian throne through papal diplomacy. His reign is characterized as relatively peaceful, with no extensive war campaigns; he focused instead on Croatia's economic and cultural development. He inherited the Croatian state at its height and ruled from the city of Knin. Medieval legends allege his assassination; his death and succession are subjects of controversy in Croatian historiography. His reign was followed by a period of anarchy, which ended with the ascension of the Hungarian Árpád dynasty and the creation of a union with Hungary.