The AK-47, officially known as the Avtomat Kalashnikova (Russian: Автома́т Кала́шникова, tr. Avtomát Kaláshnikova, lit. Kalashnikov's Automatic Rifle; also known as the Kalashnikov and AK), is a gas-operated, 7.62×39mm assault rifle, developed in the Soviet Union by Mikhail Kalashnikov. It is the originating firearm of the Kalashnikov rifle (or "AK") family.
Design work on the AK-47 began in 1945. In 1946, the AK-47 was presented for official military trials, and in 1948, the fixed-stock version was introduced into active service with selected units of the Soviet Army. An early development of the design was the AKS (S—Skladnoy or "folding"), which was equipped with an underfolding metal shoulder stock. In early 1949, the AK-47 was officially accepted by the Soviet Armed Forces and used by the majority of the member states of the Warsaw Pact.
Even after almost seven decades, the model and its variants remain the most popular and widely used assault rifles in the world because of their substantial reliability under harsh conditions, low production costs compared to contemporary Western weapons, availability in virtually every geographic region and ease of use. The AK-47 has been manufactured in many countries and has seen service with armed forces as well as irregular forces and insurgencies worldwide, and was the basis for developing many other types of individual, crew-served and specialised firearms. As of 2004, "Of the estimated 500 million firearms worldwide, approximately 100 million belong to the Kalashnikov family, three-quarters of which are AK-47s".