This man ordered the beheading of 4,500 Saxons in 
This man ordered the beheading of 4,500 Saxons in the Massacre of Verden, and he signed the Treaty of Heiligen with Danish King Hemming. This ruler deposed Tassilo III of Bavaria, and this man helped Leo III regain his position as Pope after conquering the Lombards. Einhard served as the principle biographer of this ruler, and men such as Alcuin of York brought about his namesake renaissance. The ambush of this ruler's rearguard by Basques at the Battle of Ronceveaux has been immortalized in the Song of Roland. For 10 points, name this son of Pepin the Short who was crowned on Christmas day 800 as Roman Emperor.
This man ordered the beheading of 4,500 Saxons in the Massacre of Verden, and he signed the Treaty of Heiligen with Danish King Hemming.
Charlemagne [or Charles the Great; or Carolus Magnus]