Early life and reign
Lothair was born in 795, to Louis the Pious and Emengarde of Hebsbaye. His father was the son of the reigning Emperor, Charlemagne. Little is known of Lothair's early life, which was probably passed at the court of his grandfather
Charlemagne. In 814, the elderly Charlemagne died, and left his son Louis the Pious his vast empire. The next year, Lothair, now an adult, was sent to govern Bavaria in 815 for his father the new Emperor Louis the Pious.
 In 817, Louis the Pious
 drew up his Ordinatio Imperii. In this, Louis designated Lothair as his principal heir and ordered that Lothair would be the overlord of Louis' younger sons Pippin of Aquitaine (who was 20) and Louis the German (who was 13), as well as his nephew (Lothairs Cousin)
Bernard of Italy. Lothair would also inherit their lands if they were to die childless. Lothair was then crowned joint emperor by his father at
Aachen., aged 22
 At the same time, Aquitaine and Bavaria were granted to his brothers Pippin and Louis, respectively, as subsidiary kingdoms. Following the murder of Bernard by Louis the Pious, Lothair also received the Kingdom of Italy. In 821, Lothair married
Ermengarde (d. 851), daughter of
Count of Tours.
In 822, he assumed the government of
Italy, and at Easter, 5 April 823, he was crowned emperor again by
Pope Paschal I, this time at
Rome. In November 824, Lothair promulgated a statute, the
Constitutio Romana, concerning the relations of pope and emperor which reserved the supreme power to the secular potentate, and he afterwards issued various ordinances for the good government of Italy.
On Lothair's return to his father's court, his stepmother
Judith won his consent to her plan for securing a kingdom for her son
Charles, a scheme which was carried out in 829,
 when the young prince was given
Alemannia as king. Lothair, however, soon changed his attitude and spent the succeeding decade in constant strife over the division of the Empire with his father. He was alternately master of the Empire, and banished and confined to Italy, at one time taking up arms in alliance with his brothers and at another fighting against them, whilst the bounds of his appointed kingdom were in turn extended and reduced.