Russia is the largest country in Asia by total area, including its transcontinental territory.
Russia spans roughly 17.1 million square kilometers, making it the world’s largest country. About 13.1 million square kilometers of that territory lies in Asia, chiefly across Siberia and the Russian Far East, while the remainder lies west of the conventional Europe–Asia boundary.
China is the largest country entirely within Asia, which is why some lists give China as the answer. This question specifies total area and includes transcontinental countries, so Russia is the canonical choice. Kazakhstan is also transcontinental, but it is far smaller, with most of its territory in Central Asia.
Russia’s Asian lands contain the vast Siberian forests, the world’s deepest freshwater lake, Lake Baikal, and extensive mineral and energy resources. Despite its enormous Asian territory, most of Russia’s population and major historic cities are concentrated in European Russia.