List of state leaders in 866

865 state leaders - Events of 866 - 867 state leaders - State leaders by year

Asia

• 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)
• Korea (North South States Period)
  • Balhae - Dae Geonhwang, King of Balhae (857–871)
  • Silla - Gyeongmun, King of Silla (861–875)

Europe

• Bulgaria - Boris I, Knyaz of Bulgaria (852–889)
• Byzantine Empire - Michael III (842–867)
• Caucasus
  • Principate of Iberia - Bagrat I Kuropalates, Prince of Iberia (830–876)
  • Principality of Kakheti - Gabriel, Prince of Kakheti (861–881)
• Littoral Croatia - Domagoj, Duke of Littoral Croatia (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)
  • Mercia - Burgred, King of Mercia (852–874)
  • Northumbria - Ælla, King of Northumbria (862/863–867)
  • Wessex - Æthelred, King of Wessex (865–871)
• East Francia - Louis the German, King of East Francia (843–876)
  • Duchy of Saxony -
    1. Liudolf, Duke of Saxony (844–866)
    2. Brun, Duke of Saxony (866–880)
  • Thuringia - Thakulf, Duke of Thuringia (849–873)
• West Francia - Charles the Bald, King of West Francia (843–877)
  • County of Angoulême -
    1. Emenon (863–866)
    2. Wulgrin I (866–886)
  • Anjou - Robert the Strong, Count of Anjou (861–866)
  • Duchy of Aquitaine - Ranulf I, Duke of Aquitaine (854–866)
  • Kingdom of Aquitaine -
    1. Charles the Child, King of Aquitaine (855–866)
    2. Louis the Stammerer, King of Aquitaine (866–877)
  • County of Auxerre -
    1. Robert the Strong, Count of Auxerre (864–866)
    2. Hugh the Abbot, Count of Auxerre (866–870)
  • Barcelona - Bernard II, Count of Barcelona (865–878)
  • Duchy of Brittany - Salomon (857–874)
  • County of Flanders - Baldwin I (862–879)
  • County of Maine - Gosfrid (865–878)
  • March of Neustria - Gosfrid of Maine (865–878)
  • Poitiers -
    1. Ranulf I, Count of Poitiers (854–866)
    2. Bernard of Gothia, Count of Poitiers (866–877)
  • County of Toulouse - Bernard II (865–877)
  • Tours -
    1. Robert the Strong, Count of Tours (860–866)
    2. Hugh the Abbot, Count of Tours (866–886)
  • Troyes -
    1. Rudolph I, Count of Troyes (858–866)
    2. Odo I, Count of Troyes (866–871)
  • Urgell - Solomon, Count of Urgell (848–869)
• Gascony - Sans III Mitarra, Duke of Gascony (864–893)
• Ireland - Áed Findliath, High King of Ireland (862–879)
  • Ailech - Áed Findliath, King of Ailech (c. 855–879)
  • Connacht - Mugron mac Máel Cothaid, King of Connacht (848–872)
  • Hy-Many -
  • Leinster - Dúnlaing mac Muiredaig, King of Leinster (863–869)
  • Mide - Donnchad mac Aedacain, King of Mide (864–877)
  • Munster - Cenn Fáelad hua Mugthigirn, King of Munster (861–872)
  • Osraige - Cerball mac Dúnlainge, King of Osraige (842–888)
  • Ulaid -
  • Cathalán mac Indrechtaig, co-King of Ulaid (857–871)
  • Lethlobar mac Loingsig, co-King of Ulaid (857–873)
• Italy - Louis II, King of Italy and Holy Roman Emperor (855–875)
  • Principality of Benevento - Adelchis, Prince of Benevento (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)
  • Venice - Orso I Participazio, Doge of Venice (864–881)
• Lotharingia - Lothair II, King of Lotharingia (855–869)
• Great Moravia - Rastislav, Prince of Great Moravia (846–870)
• Novgorod - Rurik, Prince of Novgorod (862–879)
• Scotland
  • Picts - Constantine I, King of the Picts (862–877)
• Serbia - Mutimir, Grand Zhupan of Serbia (850–891)
• Spain -
  • County of Aragon - Galindo Aznárez I, Count of Aragon (844–867)
  • Kingdom of Asturias -
    1. Ordoño I (850–866)
    2. Alfonso III (866–910)
    • County of Castile - Rodrigo (860–873)
  • Caliphate 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)