Serbian Medieval History
Prince Vlastimir (840s - ca. 860)
The first Serbian dynasts are legendary and known purely by name - Viseslav, succeeded by Radoslav, then Prosigoj, and finally, his great-grandson Vlastimir, whom we have more facts on. Until the times of Vlastimir, who ruled in the central part of "Baptized Serbia" with the title of "grand Zupan" (ZHOO-pan) - a hereditary prince recognized as chief among other zupans - Serbs lived under the nominal suzerainty of the Byzantine state, and generally in good terms with their Bulgarian neighbors to the east.
But during khan Presiam (836-852), Bulgars start aggressively pushing both south towards Byzantium, and east into the Morava basin. This apparently forced Vlastimir to forge more unity among the neighboring tribes, thus creating an embryonic state under his command. Few details are known, but after several years of warfare in the Morava and Kosovo regions, in the 840-850 time frame, the invasion was repulsed and the Serbs victorious.
Vlastimir's influence grew as a result of this and is evidenced by the fact he married a daughter to the prince of Travunija, bestowing various privileges on him in the process. Vlastimir died shortly after that - around the same time as his opponent Presiam - and his realm was divided, as was customary, among his three sons Mutimir, Strojimir, and Gojnik. In turn, the Bulgar throne was now replaced by Boris - known also as Michael following his acceptance of Christianity for himself and his subjects in 864. Boris' opportunistic expedition into Serbia was ambushed by Mutimir's forces, with leading Bulgars taken prisoner; their release allowed for the signing of a favorable peace.
This is also a time of systematic Christian conversion of the Serbs. While less is known about this process in Serbia compared to Bulgaria, and despite claims of baptismal efforts as early as the 7th c., it is probable that during the reigns of Vlastimir's immediate successors the effects of the missionary and literary endeavors of Cyril and Methodius and their disciples finally bore more fruit.