Final answer:
Alexander I ruled Russia from 1801 until his death in 1825. He was followed by his brother Nicholas I, who continued the conservative rule and opposed modernization.
Step-by-step explanation:
The ruler of Russia from 1801-1825 was C. Alexander I. Alexander I ascended to the throne following the reigns of significant figures like Peter the Great and Catherine the Great, both of whom contributed to the expansion and modernization of the Russian Empire. Alexander I's rule marked a period of conservatism and mysticism, influenced strongly by the upheaval of the French Revolution.
He played a pivotal role in the defeat of Napoleon's forces in 1812 and solidified his power at the Congress of Vienna. After his death in 1825, Alexander I was succeeded by his brother, Nicholas I, who continued to maintain strict control over the Russian Empire, resisting forces of modernity and promoting his conservative ideals.