Which Frankish king was crowned Emperor on Christmas Day 800?

Charlemagne, crowned by Pope Leo III in Rome - and his biographer Einhard claimed he would not have entered the church that day had he known what was coming, which is either genuine surprise or a very careful piece of political cover.

The problem was that there was already a Roman emperor, in Constantinople, and at that moment it was a woman - Irene, who had deposed and blinded her own son. The western position was that a woman could not hold the title, so the throne was vacant and could be filled. Constantinople disagreed for the next twelve years and only recognised him as emperor of the Franks, never of the Romans.

He could barely write. Einhard says he kept tablets under his pillow to practise letters and never really managed it, which did not stop him importing scholars from across Europe, standardising a legible script that is the ancestor of the lower-case letters on this page, and ordering that every monastery run a school. He also spent thirty years fighting the Saxons and had 4,500 of them executed in a day at Verden, which sits awkwardly beside the schools and rather rarely appears in the same paragraph.