Excerpts from Books and Wikipedia
"The Bulgarian khan was named Krum and under his rule--which began sometime between 796 and 803--Bulgaria swelled into a major power. Krum's southern territories lay directly against the Byzantine border, and Constantine VI's disastrous attempt to defy the Bulgarian khan Kardam, Krum's predecessor (and possibly his uncle), had clearly revealed just how vulnerable the Byzantine territory now was. . . . Around 805, Krum invaded the territory of the once-great Avars and folded it into his own, which brought his empire directly to the eastern border of Charlemagne. . . . Krum's reign began a Bulgarian dynasty that would control the country without interruption for a century. With the help of the Christianity that was already spreading from the Byzantine captives through the Bulgarian population, the descendants of Krum would begin to shape the Bulgarian horde into a state that could take its place among the kingdoms of the west." [Bauer: Medieval World, p. 400-3]