Sergei Ivanovich Mosin was a Russian firearms designer born in 1849. He is best known for creating the Mosin-Nagant, a bolt-action rifle that became the standard infantry weapon for the Russian Empire and later the Soviet Union. The rifle was widely used during various conflicts, including World War I and World War II. Mosin's design was notable for its reliability and accuracy, making it a favored choice among soldiers. The Mosin-Nagant was produced in large quantities and has become a significant part of military history, with many variants still in use or collected by enthusiasts today.