Rus' people
The title of "Khagan" for a leader of some groups of Rus' people is mentioned in several historical sources, most of them foreign texts dating from the 9th century, while three East Slavic sources date from the 11th and 12th centuries. The earliest European reference related to the Rus' people ruled by a "khagan" comes from the Frankish "Annals of St. Bertin", which refer to a group of Norsemen who called themselves "Rhos" () and visited Constantinople around 838. Fearful of returning home via the steppes, which would leave them vulnerable to attacks by the Magyars, these Rhos travelled through the Frankish Empire accompanied by Greek ambassadors from the Byzantine emperor Theophilus. When questioned by the Frankish Emperor Louis the Pious at Ingelheim, they stated that their leader was known as "chacanus" (hypothesized to be either the Latin word for "Khagan" or a deformation of Scandinavian proper name "Håkan"), that they lived far to the north, and that they were Swedes ("comperit eos gentis esse sueonum").