Final answer:
The Emperor of Russia in 1812 was Alexander I, who was in power during the defeat of Napoleon's invading forces in Russia.
Step-by-step explanation:
Emperor of Russia in 1812
The emperor of Russia in 1812 was Alexander I. He ruled the Russian Empire from 1801 until his death in 1825. During his reign, Alexander I led Russia through the period of the Napoleonic Wars, which included the famous 1812 campaign where the Russian Army and winter conditions played critical roles in the defeat of Napoleon's Grand Army. Alexander I was known for his conservative policies and attempts to maintain the monarchy's power against the forces of modernity which were transforming Europe at the time.
Defeat of Napoleon's Armies
It was primarily under the leadership of Alexander I that Russia saw off the invasion by Napoleon. The endurance of Russian forces and the harsh winter led to the retreat and eventual ruin of the French invading army. This victory elevated Alexander's prestige and positioned him as one of the influential leaders in Europe, particularly during the post-war negotiations at the Congress of Vienna.