Sviatoslav I of Kiev
According to the historians John Skylitzes and Leo the Deacon, Kalokyros was the son of a "strategos" of Chersonesos. In 967 or 968, Nikephoros II bestowed upon him the title of "patrikios" and dispatched him to the court of Sviatoslav I of Kiev in order to persuade him to launch an invasion of the First Bulgarian Empire, with which Byzantium was at war. Kalokyros was to pay Sviatoslav 15,000 pounds of gold to defray the expense of the voyage.