Who was alive in 820?

271 well-known people were alive in 820, including Muḥammad ibn Musa al-Khwarizmi, Ādi Shankara, Louis the Pious. Here are the 80 most notable:

Muḥammad ibn Musa al-Khwarizmi (780–850) — 9th-century Persian mathematician and astronomer
Ādi Shankara (788–820) — An Indian philosopher and theologian who consolidated the doctrine of Advaita Vedanta and revitalized Sanskrit scholasticism.
Louis the Pious (778–840) — King of the Franks
Al-Kindi (801–870) — Muslim Arab philosopher, mathematician and physician (c.801–873)
Gregory IV (795–844) — Pope and bishop of Rome from 827 to 844
Muḥammad ibn Ismaeel al-Bukhārī (810–870) — Persian Islamic scholar (810-870)
John VIII (820–882) — Head of the Catholic Church from 872 to 882
Adrian II (792–872) — pope
Leo IV (790–855) — pope of the Catholic Church
Formosus (816–896) — pope
Al-Shafi'i (767–820) — Arab Muslim theologian, writer and scholar (767–820)
Paschal I (775–824) — pope
Eugene II (780–827) — pope
Ahmad ibn Hanbal (780–855) — Muslim jurist and theologian (780–855)
Benedict III (810–858) — pope (810-858)
Nicholas I (820–867) — pope
Sergius II (790–847) — pope
Anastasius III (801–) — pope
Valentine (780–827) — pope
Lothair I (795–855) — Emperor of the Carolingian Empire from 817 to 855
Johannes Scotus Eriugena (800–877) — Irish Catholic philosopher and theologian (c. 800 – c. 877)
Louis the German (806–876) — King of East Francia from 843 to 876
al-Maʾmun (786–833) — Abbasid caliph (786–833, r. 813–833)
Basil I (811–886) — Byzantine emperor from 867 to 886
Bai Juyi (772–846) — Chinese poet of the Tang Dynasty (772-846)
Ragnar Lodbrok (801–850) — legendary king of Denmark and Sweden
Al-Jahiz (775–868) — Arabic writer (776–869)
Ecgberht (771–839) — King of Wessex
Abbas Ibn Firnas (810–887) — 9th century astronomer and physician
Photios I of Constantinople (820–900) — 9th Century Ecumenical Patriarch of Constantinople
Han Yu (768–824) — Chinese historian, poet, philosopher and politician (768–824)
Kenneth MacAlpin (810–858) — King of the Picts
Michael I Rangabe (770–844) — Byzantine emperor
Leo V the Armenian (775–821) — Byzantine emperor (lived 775–820)
Theophilos (813–842) — Byzantine emperor from 829 to 842
Michael II (770–829) — Byzantine emperor
Abd ar-Rahman II (792–852) — Emir of Cordoba from 822 to 852
Einhard (774–840) — Frankish scholar and courtier (c. 775 – 840)
Al-Mu'tasim (796–842) — 8th Abbasid Caliph. (r. 833–842)
Kūkai (774–835) — Japanese Buddhist monk and calligrapher, the founder of the Shingon school (774–835)
Domnall mac Ailpín (812–862) — King of the Picts from 858 to 862
Abu Dawud al-Sijistani (817–888) — 9th-century Persian Hadith compiler
Babak Khorramdin (798–838) — 9th-century Iranian revolutionary leader
Al-Baladhuri (820–892) — Abbasid-era Muslim historian (820-892)
Rabanus Maurus (780–856) — archbishop of Mainz and writer (d. 856)
Theodora (815–867) — 9th-century Byzantine empress, wife of Theophilos
Fatima al-Fihriya (800–880) — Legendary founder of the al-Qarawiyyin mosque
al-Yaʿqubi (801–905) — 9th-century Arab geographer and historian
Constantine II of Scotland (801–) — 10th-century king of Scotland (Alba)
Al-Wathiq (812–847) — 9th Abbasid Caliph (r. 812–847)
Ibn Khordadbeh (820–912) — Persian geographer and official (died 913)
Ansgar (801–865) — missionary to Denmark and later Archbishop of Hamburg-Bremen
Du Mu (803–852) — Chinese calligrapher, poet and politician (803–852)
Abu Tammam (805–846) — Muslim Arab poet of Abbasid era (died 850)
Kassia (810–865) — Byzantine abbess, poet, composer, and hymnographer
Muhammad al-Jawad (811–835) — ninth of the Twelve Imams of Twelver Shi'ism
Nikephoros I of Constantinople (750–828) — patriarch of Constantinople
Alfonso II of Asturias (759–842) — King of Galicia (c. 760 – 842)
Theodore the Studite (759–826) — Byzantine saint
Al-Hakam I (771–822) — Emir of Córdoba from 796 to 822
Abu Ma'shar al-Balkhi (787–886) — Persian astrologer and philosopher (787–886)
Bayazid Bastami (804–848) — 9th century Persian Sufi mystic
Álmos, Grand Prince of the Magyars (820–895) — kende or gyula of the Hungarians (fl. 9. century)
Emperor Saga (786–842) — Emperor of Japan
Dhu'l-Nun al-Misri (796–860) — Sufi saint
Pepin I of Aquitaine (797–838) — 9th-century Frankish king
Hunayn ibn Ishaq (808–873) — Arab Christian scholar, physician and scientist (809–873)
Ziryab (777–857) — 9th-century poet and musician
Ramiro I of Asturias (791–850) — King of Asturias
Thomas the Slav (800–823) — Byzantine military commander (c. 760–823)
Emperor Heizei (774–824) — Emperor of Japan
Ninmyō (810–850) — Emperor of Japan
Emperor Junna (786–840) — Emperor of Japan
Nennius (800–900) — Welsh monk and historian
Philip (800–) — Italian priest, antipope in 768
Rastislav (820–) — Grand Duke of Moravia
Li Shangyin (813–858) — Chinese poet and writer
Yuan Zhen (779–831) — Chinese poet
Methodios I of Constantinople (788–847) — Patriarch of Constantinople
Jayavaraman II (800–900) — 9th-century king of Cambodia

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