Which country was ruled by Basil II the Bulgar-slayer?

At the start of the second millennium, Basil attacked Bulgarians in order to restore territories the Empire had lost long before. He was said to have captured 15,000 prisoners and blinded 99 of every 100 men, leaving one one-eyed man in each cohort to lead the rest back home. Samuel, the ruler of Bulgaria was so shocked seeing his blinded army, that he died two days later.