Khan Asparoukh 
In the mid to late 600s, a tribe of mounted horse warriors ethnically related to the Huns and Avars continued their migration from central Asia. Although smaller groups of Bulgars had already been present in the area, a large force of about 250 000 arrived at the Danube delta in about 680. They soon pressed southwards into the Slav territory, led by their khan, or chief, Asparoukh, and took control of land as they went.
Byzantine Emperor Constantine IV officially recognised the powerful new force to the north, and Khan Asparoukh firmly established the First Bulgarian Kingdom in 681, which lasted until 1018. With an administration centered in the northeastern city of Pliska, the First Bulgar Khanate stretched roughly from the Carpathians in the north to the Balkan Mountain range in the south and is generally considered the first Slavic state in history.
The more numerous Slavs did eventually assimilate the Bulgars into their culture, but fuelled by the Bulgars' fierce warlike nature, a series of khans expanded the territory. Under the leadership of Khan Krum (803-814), the Byzantine capital of Constantinople (present-day Istanbul) was almost captured in one of the many conflicts between the two powers. The greatest land gains were made under the rule of Krum "The Terrible", whose nickname was partially due to having the skull of the conquered Byzantine Emperor Nicephorus made into a wine goblet (interestingly today one of Bulgaria's finest wines is named after the khan!). By the end of his reign, Krum's empire stretched from the Rila Mountains in the west to the Rodope Mountains in the south.
By the ninth century, Macedonian lands were also under Bulgarian control, and Khan Omurtag (852-889) forged a peace treaty with the Byzantines, paving the way for increased trade of goods, ideas and culture. Following Bulgarian kings were called tsars, or caesars, after the Byzantine tradition, and in 865, Tsar Boris I was converted to Orthodox Christianity. He then adopted the religion as the official faith of the Bulgarian kingdom, where the majority of the dominant Slav population had already been converted.
