Svatopluk I of Moravia

Svatopluk governed a principality under his uncle Rastislav in the 860s, then dethroned him in 870 and handed him over to Louis the German. Within a year the Franks imprisoned Svatopluk too, but when the Moravians rebelled he was released to lead them and routed the invaders. The 874 peace treaty at Forchheim forced him to pay tribute to East Francia, yet he expanded aggressively beyond Frankish reach and even invaded the March of Pannonia in 882. He cultivated Rome - Pope Stephen V called him "King" in 885 - but after Methodius died in 886, Svatopluk expelled his Slavonic-rite disciples to placate the German clergy. His state was a patchwork of principalities and conquests spanning parts of what are now Czechia, Slovakia, Poland, and Hungary. Shortly after his death the whole structure collapsed under his sons' power struggle and the Hungarian onslaught.