Basil II (c. 958-1025), Byzantine emperor (976-1025), the greatest ruler of the Macedonian dynasty. The son of Emperor Romanus II, he reigned jointly with his brother Constantine VIII after the death of the usurper John I Tzimisces in 976, but Constantine never took an active role in government. Basil's greatest achievements were the conquest of Armenia in the east and the destruction of the Bulgarian Empire, which threatened Byzantium on the west. He waged war on the Bulgars for nearly two decades. Defeating (1014) the Bulgarian Tsar Samuel, he subjected his people to Byzantine rule and was given the surname Bulgaroctonos (Slayer of Bulgars). The Byzantine Empire began to decline after Basil's death.