Zdeslav (Sedesclavus) was, along with Peter and Muncimir, one of the three sons of the Croatian duke Trpimir. After duke Domagoj came to power and had his eldest brother Peter killed Zdeslav and Muncimir, they hid in Constantinople. According to the Venetian Chronicle of the Venetian chronicler Ivan the Deacon, Zdeslav ascended the throne after Domagoj’s death with the support of the Byzantine Emperor Basil I. During his reign he acted in many ways for Byzantine interests in Croatia. He immediately had the sons of duke Domagoj expelled as possible contenders for the title. During the reign of Basil I, the Byzantine “theme of Dalmatia” was founded on the Adriatic, which included the cities and islands of Osor, Krk, Rab, Zadar, Trogir, Split, Dubrovnik and Kotor, as well as some smaller places on the southern Adriatic coast and inland. At the same time, in an effort to secure Byzantine possessions on the eastern Adriatic coast, he obliged Dalmatian towns to pay a tax to the Croatian duke (instead of the Byzantine strategist) in the name of peaceful enjoyment of land holdings and preservation of peace (Split 200, Zadar 110, Trogir, Osor, Rab and Krk 100 gold coins each). Basil also reformed the church organization and removed the Dalmatian bishops from the papal jurisdiction and subordinated them to the patriarch of Constantinople. Despite the influence of the Byzantine emperor, Zdeslav maintained good relations with the pope in Rome. This is evidenced by the fact that Pope John VIII in his letter adresses Zdeslav as „his beloved son Sedeslav, the glorious duke of the Slavs” in which he asked him „to take care of his legate on the way to Bulgaria.” Zdeslav was not in power for a long time because he was killed in 879 and Branimir came to power.
Ivan the Deacon states that “a Slav named Branimir, after killing Zdeslav, appropriated his principality” (“ipsius ducatum usurpavit”). Branimir’s origin is not exactly known, but from the inscriptions and grants, as well as from the form of the name, it can be concluded that he was from the vicinity of Dubrovnik. His inscription from the pre-Romanesque church in Muć from 888 does not bring any royal inscription. On the inscription of the architrave of the altar partition from the church of St. Michael in Nin (879 – 892) is called “Bra (nnimero dux Sclavorum”). The fragments from the pre-Romanesque church near Skradin read “(Bra) nimero duce (m) Sclavitnor (m), and similarly on other inscriptions with his name. In Šopota near Benkovac it was written “Branimero com … dux Chruatoru (m)”. In the Gospel of Chedda it is written: “Brannimero comiti Mariosa cometissa” which refers to Branimir and probably to his wife Maria. It is obvious that the Croatian and Slavic names are used as synonyms, and Branimir probably bore the titles of ban (comes) and the title of duke (dux) at the same time.
In order to consolidate his power over Byzantium, Branimir turned to Pope John VIII, and with that move left the Byzantine political and ecclesiastical atmosphere. The Pope happily accepts the wish of duke Branimir because Rome also wanted to regain its jurisdiction over the eastern Adriatic. Due to good relations with the Pope, Branimir especially protected the Church and spread Christianity, so many churches were built behind him.
In a letter dated June 7, 879, Pope John VIII. praises Branimir for “returning to the Roman Church” and calls him “beloved son Branimir”, and at the same time writes a similar letter to the Bishop of Nin Theodosius, and to the clergy and all the people, his “dear sons“. Similar letters, dated between 7 and 14 June 879, the pope sent to the Bulgarian king Boris I, the great Moravian prince Svatopluk and the archbishop Methodius in Pannonia. However, the Croats did not show this loyalty to Rome directly and without hesitation, but through the Patriarchate of Aquileia. In this way Branimir, like the Frankish rulers, retained greater independence in appointing bishops in his area.
In 887, near Makarska, Branimir, in cooperation with the people of Neretva, inflicted a heavy defeat on the Venetian navy, during which the Venetian doge Peter Candian was killed. After this defeat, the Venetians undertook to pay Croats a tax for the peaceful navigation of the Adriatic (“solitus census”), which would last until the end of the 10th century.
Branimir was succeeded around 892 by Muncimir, the son of Prince Trpimir and Zdeslav’s brother. He inherited an independent and strong state from his predecessor Branimir, and did not emphasize any ruler as his supreme leader. He bore the title “dux Croatorum” as did his father Trpimir, but also the title princeps, both of which emphasized his sovereignty. In a document from 892, he emphasized his hereditary right to power, emphasizing that he sat on the paternal throne. In that document, the verdict in the dispute over the church of St. George on Putalj between the Bishop of Nin and the Archbishop of Split. Muncimir was accompanied by prefects and other dignitaries, from whose names it can be concluded that the court of the Croatian ruler was arranged according to the model of the Carolingians. He dined in Bijaći near Trogir. Muncimir is also mentioned on an inscription from the church of St. Luke in Uzdolje near Knin, dated 895. Dating according to the years of the Christian era speaks of the strong influence of Rome on the Church in Croatia. Probably already during Muncimir’s reign, 905–906, the Slavic population of Pannonia fled to Croatia before the Magyar (Hungarian) invasions. He was succeeded by Tomislav, but nothing is known about their family ties.