List of state leaders in 821

820 state leaders – Events of 821 – 822 state leaders – State leaders by year

Asia

• China (Tang Dynasty) - Muzong, Emperor of Tang China (821–824)
• Gurjara - Nagabhata II, Pratihara King of Gurjara (805–833)
• Japan (Heian Period) - Emperor Saga, Emperor of Japan (809–823)
• Korea (North South States Period)
  • Balhae - Seon, King of Balhae (818–830)
  • Silla - Heondeok, King of Silla (809–826)

Europe

• Bulgaria - Omurtag, Khan of the Bulgars (814–831)
• Byzantine Empire - Michael II, Roman Emperor (820–829)
• Caucasus
  • Principate of Iberia - Ashot I Kuropalates (c. 813–830)
  • Principality of Kakheti - Grigol, Prince of Kakheti (786–827)
• Kingdom of Denmark - Horik I (813–854)
• England (Heptarchy) - Cenwulf of Mercia, Bretwalda (796–821)
  • Kingdom of Essex - Sigered, Duke of Essex (812–825)
  • Mercia -
    1. Cenwulf, King of Mercia (796–821) and East Anglia (c. 799–821) and King of Kent (807–821)
    2. Ceolwulf, King of Mercia (821–823) and East Anglia (c. 821–823) and King of Kent (821–823)
  • Northumbria - Eanred, King of Northumbria (810–841)
  • Wessex - Egbert, King of Wessex (802–839)
• Frankish Empire -
  • Louis the Pious, King of the Franks and Senior Holy Roman Emperor (814–840)
  • Lothair I, King of Italy and Junior Holy Roman Emperor (817–855)
  • Aquitaine - Pepin I of Aquitaine, King of Aquitaine (817–838)
    • Auvergne - Guerin of Provence, Count of Auvergne (819–839)
    • Gascony - Aznar Sánchez, Duke of Gascony (819–836)
    • Toulouse - Berengar the Wise, Count of Toulouse (816–835)
  • County of Barcelona - Rampon (820–825)
  • Bavaria - Louis the German, King of Bavaria (817–843)
  • Littoral Croatia -
    1. Borna of Croatia, Prince of Littoral Croatia (c. 810–821)
    2. Vladislav of Croatia, Duke of Littoral Croatia (c. 821–835)
  • County of Nantes - Lambert I (818–831)
  • County of Urgell - Aznar I Galíndez (820–834)
• Ireland - Conchobar mac Donnchada, High King of Ireland (819–833)
  • Ailech - Murchad mac Máele Dúin, King of Ailech (819–823)
  • Connacht - Diarmait mac Tommaltaig, King of Connacht (815–833)
  • Uí Maine -
  • Leinster - Muiredach mac Ruadrach, King of Leinster (808–829)
  • Kingdom of Mide - Conchobar mac Donnchado (803–833)
  • Ulaid - Máel Bressail mac Ailillo, King of Ulaid (819–825)
• Italy - Lothair I, King of Italy and Junior Holy Roman Emperor (818–855)
  • Principality of Benevento - Sico of Benevento (817–832)
  • Papal States - Pope Paschal I (817–824)
  • Republic of Venice - Agnello Participazio, Doge of Venice (811–827)
• Pannonian Croatia - Ljudevit Posavski, Duke of the Pannonian Croats (c. 810–823)
• Scotland
  • Picts - Óengus, King of the Picts (820–834)
• Spain -
  • County of Aragon - García Galíndez (820–833)
  • Kingdom of Asturias - Alfonso II (791–842)
  • Caliphate of Córdoba - al-Hakam I (796–822)
• Wales -
  • Kingdom of Gwynedd - Hywel ap Rhodri Molwynog (816–825)
  • Kingdom of Powys - Cyngen ap Cadell (808–855)