Short answers, pulled from the story.
Most scholars accept 748 as the correct birth year, though Einhard claimed he died at age 72 in 814 suggesting 742. Modern historians like Karl Ferdinand Werner and Matthias Becher argue that annalists recorded the start of the year from Easter rather than January 1st shifting the actual birth date to April 748.
Charlemagne had 4,500 Saxon prisoners beheaded after Widukind defeated a Frankish army in Saxony. He issued the Capitulatio de partibus Saxoniae immediately which included the death penalty for pagan practices to suppress Saxon identity.
Pope Leo III proclaimed Charlemagne emperor of the Romans inside St. Peter's Basilica on Christmas Day 800. This coronation marked the first time an emperor ruled from the west since Romulus Augustulus in 476 and created immediate conflict with the Eastern Roman Empire in Constantinople.
An estimated 90,000 manuscripts were produced during the 9th century alone as scriptoria in monasteries focused on copying new and old works. The Carolingian minuscule script was developed and popularised influencing Renaissance typefaces while students learned basic Latin literacy grammar arithmetic and other liberal arts subjects.
Harun al-Rashid provided an elephant named Abul-Abbas which arrived at Aachen in 802 after Charlemagne requested it as an early sign of friendship. Harun also sought to undermine Charlemagne's relations with Byzantines by giving him nominal rule of the Church of the Holy Sepulchre in Jerusalem.
Charlemagne died on the morning of the 28th of January 814 after developing pleurisy and being bedridden for seven days. Louis arrived 30 days after his father's death taking charge of the palace and empire before it was divided among sons into West East and Middle Francia by Treaty of Verdun.