It all started when Mikhail Kalashnikov, a soldier in the Red Army, was injured in the Battle of Bryansk in 1941. While he was in the hospital, he entered a competition and began to develop a rifle that would work with new caliber of bullet. He lost the contest, but he had a team now(one member would become his wife). In 1945, even though the war ended, he continued to work on a rifle. The first "Kalashnikov" style weapon was a successful prototype known as the AK-46. But they revised and improved it, creating the AK-47 in 1947 (which is how it got it's name). The AK in the name stood for "Avtomat Kalashikova". The Red Army liked the reliability of the gun, so it was formally accepted for use in them in 1949.
The gun was tough, rugged and reliable. It is still used in many countries today as the main assault rifle. One of the main reasons it was so successful was because of Kalashnikov's lack of knowledge on fully auto rifles. It worked by when they fired the first shot, some of the gases would go into another tube in the barrel, which would send the gases back, pulling back the hammer and loading the next round. The AK-47 is a piece of rifle history.