List of state leaders in 866

This is a list of heads of state, government leaders, and other rulers in the year 866.

Asia

• Champa – Vikrantavarman III (854–875)
• China (Tang dynasty) – Emperor Yizong (859–873)
• Pratihara Empire – Mihira Bhoja I (c. 836–886)
• Japan (Heian period) – Emperor Seiwa (858–876)
• Khmer Empire – Jayavarman III (850–877)
• Khorasan (Saffarid dynasty) – Ya'qub ibn al-Layth al-Saffar (858–876)
• Korea (North South States Period)
  • Balhae – Dae Geonhwang (857–871)
  • Unified Silla – Gyeongmun (861–875)
• Rashtrakuta – Amoghavarsha I (814–878)

Europe

• First Bulgarian Empire – Boris I, Knyaz of Bulgaria (852–889)
• Byzantine Empire – Michael III (842–867)
• Caucasus
  • Principality of Iberia – Bagrat I Kuropalates (830–876)
  • Principality of Kakheti – Gabriel (861–881)
• Duchy of Croatia – Domagoj (864–876)
• Kingdom of Denmark –
  1. Horik II (854–c. 866)
  2. Bagsecg (c. 866–c. 871)
• England (Heptarchy) –
  • Kingdom of East Anglia – Edmund the Martyr (854–869)
  • Kingdom of Mercia – Burgred (852–874)
  • Kingdom of Northumbria – Ælla (862/863–867)
  • Kingdom of Wessex – Æthelred (865–871)
• East Francia – Louis the German (843–876)
  • Duchy of Saxony –
    1. Liudolf (844–866)
    2. Bruno (866–880)
  • Duchy of Thuringia – Thachulf (849–873)
• West Francia – Charles the Bald (843–877)
  • County of Angoulême –
    1. Emenon (863–866)
    2. Wulgrin I (866–886)
  • County of Anjou – Robert the Strong (861–866)
  • Duchy of Aquitaine – Ranulf I (854–866)
  • Kingdom of Aquitaine –
    1. Charles the Child (855–866)
    2. Louis the Stammerer (866–877)
  • County of Auxerre –
    1. Robert the Strong (864–866)
    2. Hugh the Abbot (866–870)
  • County of Barcelona – Bernard II (865–878)
  • Duchy of Brittany – Salomon (857–874)
  • County of Flanders – Baldwin I (862–879)
  • County of Maine – Gauzfrid (865–878)
  • March of Neustria – Gauzfrid, Count of Maine (865–878)
  • County of Poitiers –
    1. Ranulf I (854–866)
    2. Bernard of Gothia (866–877)
  • County of Toulouse – Bernard II (865–877)
  • County of Tours –
    1. Robert the Strong (860–866)
    2. Hugh the Abbot (866–886)
  • County of Troyes –
    1. Rudolph I (858–866)
    2. Odo I (866–871)
  • County of Urgell – Solomon (848–869)
• Duchy of Gascony – Sans III Mitarra (864–893)
• Ireland – Áed Findliath, High King of Ireland (862–879)
  • Kingdom of Ailech – Áed Findliath (c. 855–879)
  • Kingdom of Connacht – Mugron mac Máel Cothaid (848–872)
  • Uí Maine –
  • Kingdom of Leinster – Dúnlaing mac Muiredaig (863–869)
  • Kingdom of Mide – Donnchad mac Aedacain (864–877)
  • Kingdom of Munster – Cenn Fáelad hua Mugthigirn (861–872)
  • Kingdom of Osraige – Cerball mac Dúnlainge (842–888)
  • Kingdom of Ulaid –
  • Cathalán mac Indrechtaig, co-King (857–871)
  • Lethlobar mac Loingsig, co-King (857–873)
• Kingdom of Italy – Louis II (855–875)
  • Principality of Benevento – Adelchis (854–878)
  • County of Capua – Landulf II (863–879)
  • March of Friuli – Unruoch III (863–874)
  • Duchy of Gaeta –
    1. Constantine, Hypatus of Gaeta (839–866)
    2. Docibilis I, Hypatus of Gaeta (866–906)
  • Duchy of Naples – Gregory III (864–870)
  • Papal States – Pope Nicholas I (858–867)
  • Principality of Salerno – Guaifer (861–880)
  • Duchy of Spoleto – Lambert I (860–871)
  • March of Tuscany – Adalbert I (847–886)
  • Republic of Venice – Orso I Participazio, Doge of Venice (864–881)
• Kingdom of Lotharingia – Lothair II (855–869)
• Great Moravia – Rastislav (846–870)
• Novgorod – Rurik, Prince of Novgorod (862–879)
• Scotland
  • Kingdom of the Picts – Constantine I (862–877)
• Principality of Serbia – Mutimir, Grand Župan (850–891)
• Spain –
  • County of Aragon – Galindo Aznárez I (844–867)
  • Kingdom of Asturias –
    1. Ordoño I (850–866)
    2. Alfonso III (866–910)
    • County of Castile – Rodrigo (860–873)
  • Emirate of Córdoba – Muhammad I (852–886)
  • Kingdom of Pamplona – García Íñiguez (851/852–882)
• Wales –
  • Kingdom of Gwynedd – Rhodri Mawr (844–878)
  • Kingdom of Powys – Rhodri Mawr (855–878)