Sergei Gavrilovich Simonov (Russian: Серге́й Гаври́лович Си́монов; 4 October 1894 – 6 May 1986) was a Soviet weapons designer who is considered one of the fathers of the modern assault rifle.

Born in 1894 in Fedotovo (now Melekhovo), Simonov began work in a foundry immediately after completing his elementary school studies.

By the end of World War I, after completing a basic technician's course of instruction, he began working on a pioneering automatic rifle designed by Vladimir Grigoryevich Fyodorov, the Fedorov Avtomat.

After the Russian Revolution, Simonov continued further at the Moscow Polytechnic Institute, graduating in 1924 to work at Russia's giant Tula Arsenal.

After some tweaking, it was officially adopted and designated the 7.62 Samozaryadnyi Karabin Sistemy Simonova Obrazets 1945 g. (translated, "7.62 Self-loading Carbine System Simonov model year 1945") or SKS-45, and chosen as the ideal replacement for the SVT-40.