Tomislav was a Croatian ruler who, based on the documents, ruled Croatia from around year 910. (in 914. Tomislav is first mentioned in the document “Historia Salonitana” as dux (duke). He probably belonged to a dynasty that originated from the Croatian duke Trpimir (845.-864.), but it is not possible to exactly determine the relationship with his predecessors.
Initially he ruled as the duke of Coastal Croatia, but he extended his rule to the north (Pannonian Croatia) and east (to Bosnia). In his time, a great threat in Central Europe was posed by the Hungarians (Magyars) whose incursions he repulsed. In 927. somewhere in Bosnia he defeated the Bulgarian emperor Simeon. In his work “De administrando imperio” the Byzantine emperor Constantine VII. Porphyrogenitus points out that Croatia at that time was extremely militarily powerful and that it could raise a large number of cavalry and infantry on land and large (sagenas) and small ships (conduras) at sea. Spurs were found in most of the graves of warriors from that time which speaks of cavalry as an important element of the Croatian army. Tomislav completely took control of the coastal cities and islands that were until then under Byzantine rule and he collected taxes from them. Trade between Dalmatian towns intensified and there do not appear to have been any major conflicts at sea in that time. In general, Tomislav has consolidated his rule. Military and economic power of Croatia was growing at the time.
Tomislav is first mentioned as a king (lat. rex) in a letter written to him by Pope John X. In the year 925. “… Tamisclao, regi Crouatorum …” (“… to Tomislav, king of the Croats …”).
In 925. and 928. two church councils were held in Split. At the first council in 925. it was to decide on the use of the slavic language in worship and church powers, and on the dispute over the right to the position of metropolitan between the bishop of Nin (Grgur), the bishop of Zadar (Formin), and the archbishop of Split (Ivan). At the end, archbishop Ivan was elected as metropolitan. The bishop of Nin, Grgur later appealed to the pope against this decision and in 928. a new council was convened which again confirmed Ivan as metropolitan and the diocese of Nin was abolished. Tomislav attended the assembly in 925. and very probably in 928. The note in front of the text of the conclusions of the assembly from 925. reads: “… consulatu peragente in provincia Chroatorum et Dalmatiarum finibus Tamisclao rege …” (“… king Tomislav ruled in the province of the Croats and the borders of Dalmatia “) and in the 7th canon of the note: “… rex et proceres Chroatorum… ” („…king of the Croats and the croatian nobles…“). Tomislav died probably in 928. and was succeeded by his brother Trpimir II.
Among the Croatian people and in historiography Tomislav is most often seen as the first Croatian king, given the information I have presented, but the opinions of modern historians are still divided. What is certain is that in his time Croatia was militarily and politically very powerful (Hungarian and Bulgarian incursions were repulsed) and the influence of the Croatian ruler and the territory of the state was further expanded (he ruled coastal towns and islands, affiliated Pannonian Croatia and Bosnia).