Lothair I (9th. C. Frankish: Ludher and Medieval Latin: Lodharius; Dutch and Medieval Latin: Lotharius; German: Lothar; French: Lothaire; Italian: Lotario; 795 – 29 September 855) was a 9th-century Emperor of the Carolingian Empire (817–855, with his father until 840) and King of Italy (818–855) and Middle Francia (843–855).
Lothair I was the eldest son of the Carolingian emperor Louis I and his wife Ermengarde of Hesbaye, daughter of Ingerman the duke of Hesbaye. On several occasions, Lothair led his full-brothers Pepin I of Aquitaine and Louis the German in revolt against their father to protest against attempts to make their half-brother Charles the Bald a co-heir to the Frankish domains. Upon the father's death, Charles and Louis joined forces against Lothair in a three-year dynastic war (840–843). The struggles between the brothers led directly to the breakup of the Frankish Empire assembled by their grandfather Charlemagne, and laid the foundation for the development of modern France and Germany.
thumb|right|200px|Denier of Lothair I, struck in [[Dorestad (Middle Francia) after 850]]
thumb|right|200px|Medallion presumed to be of Lothair, from the binding of the [[Lothair Psalter in the British Library]]
When Louis the Pious was dying in 840, he sent the imperial insignia to Lothair, who, disregarding the various partitions, claimed the whole of the Empire. He was 45 years old when his father died. Negotiations with his brother Louis the German and his half-brother Charles, both of whom resisted this claim, were followed by an alliance of the younger brothers against Lothair. A decisive battle was fought at Fontenay-en-Puisaye on 25 June 841, when, in spite of his
Death and aftermath
thumb|right|200px|13th-century stained glass depiction of Lothair, [[Strasbourg Cathedral]]
In 855 he became seriously ill, and despairing of recovery renounced the throne, divided his lands among his three sons, and on 23 September entered the monastery of Prüm, where he died six days later. He was buried at Prüm, where his remains were found in 1860.
The same year, Lothair's kingdom was divided between his three sons