List of state leaders in 866

Asia

• Bohai/Balhae - Da Qianhuang/Dae Geon-hwang, King of Bohai/Balhae (northeast Asia) (857-871)
• China (Tang Dynasty) - Yizong, Emperor of Tang China (859-873)
• Gurjara - Mihira Bhoja I, Pratihara King of Gurjara (c. 836-886)
• Japan - Emperor Seiwa, emperor of Japan (858-876)
• Silla - Gyeongmun, King of Silla (861-875)

Europe

• Asturias -
1. Ordoño I, King of Asturias (850-866)
2. Alfonso III the Great, King of Asturias (866-910)
• Bulgaria - Boris I, Knyaz of Bulgaria, (852–889)
• Danelaw - Guthrum, King of the Danelaw (854–890)
• East Anglia¹ - Edmund, King of East Anglia (855–870)
• England (Wessex) - Ethelred of Wessex, Bretwalda (865–871)
• Friesland - Rorik, King of the Danish Vikings in Friesland (850-880)
• Mercia - Burgred, King of Mercia (852–874)
• Northumbria¹ - Osbert, King of Northumbria (849–867)
• Ireland - Aedh Finnliath, High King of Ireland (861–876)
• Scotland - Constantine I, King of Scots and Picts (862–877)
• Strathclyde - Arthgal f Dyfnwal, King of Strathclyde (816–872)
• Venice - Orso I Participazio, Doge of Venice (864-881)
• Wales - Rhodri Mawr ap Merfyn, King of Gwynedd (844–878)
• Western Francia - Charles the Bald, King of Western Francia (843-877)

Notes

1. Though East Anglia, Northumbria and Mercia are traditionally perceived to have been in the heptarchy they were largely independent kingdoms until its conquest by the Danes in 869 and 867, respectively - where Mercia was conquered by Wessex in 874. All other members of the heptarchy had been conquered by Wessex and by this time had no form or king.