Simeon I of Bulgaria
He had a crucial role in the Hungarian Conquest (Honfoglalás). In 892/893 together with Arnulf of Carinthia he attacked Great Moravia to secure the eastern borders of the Frankish Empire. Arnulf gave him all the captured lands in Moravia. Kurszán also occupied the southern part of Hungary that had belonged to the Bulgarian Kingdom. He entered into an alliance with the Byzantine emperor Leo VI after realizing the country's vulnerability from the south. Together they surprisingly defeated the army of Simeon I of Bulgaria.