Major General Sergio Ivanovich Mosin (Cyrillic: Серге́й Ива́нович Мо́син) was a Russian military officer and designer that was associated with the Tula Arms Plant.
Mosin was born the son of a retired Second Lieutenant in Ramon in 1849, and entered himself into the Mikhailovsky Artillery School in 1872; he graduated from said academy in 1875 and sought employment at the Tula Arms Plant.
Mosin worked his way up the ranks at the Tula Arms Plant, eventually becoming the acting chairman of the plant's admission division. After his abilities were recognized, he was asked to oversee the production of rifles at the Sestroretsk and Izhevsk Arms Factories.
He met Belgian gunsmith Léon Nagant in 1889 and improved his design, culminating in the Mosin-Nagant. He also worked as an employee of the Sestroretsk Arms Plant. Mosin died in Sestroretsk in 1902 of pneumonia and is buried in the area.
Sergei Mosin is most well known for the design of the Mosin-Nagant rifle.