The AR-15, originally designed by Eugene Stoner in the late 1950s, is a lightweight, air-cooled, gas-operated semi-automatic rifle. It is chambered for various cartridges, including the .223. The AR-15 gained popularity as a civilian firearm, with versions such as the civilian AR-15 and military M16. Known for modularity, it's widely used in the civilian market, law enforcement, and military. The AR-15's legacy includes its adaptability and influence on modern rifle design.