Metal Slug (Japanese: メタルスラッグ, Hepburn: Metaru Suraggu) is a Japanese multimedia franchise and run and gun video game series originally created by Nazca Corporation before merging with SNK in 1996 after the completion of the first game in the series. Spin-off games include a third-person shooter to commemorate the 10th anniversary of the series and a tower defense game for the mobile platform. Originally created for Neo-Geo arcade machines hardware (MVS) and the Neo-Geo home game consoles (AES) hardware, the original games have also been ported to other consoles and mobile platforms throughout the years, with several later games created for various other platforms. The games focus on the Peregrine Falcon Squad, a small group of soldiers who fight against a rebel army, aliens, zombies, mummies and various other forces intent on world domination.
The first game's story involved the Peregrine Falcon (PF) Squad, a small but skilled team of soldiers serving under the Regular Army's special operations division, who fight against the army of General Donald Morden in order to prevent a massive coup d'état and the creation of a New World Order. Later games featured characters from the Sparrows Unit, which is under the control of the Regular Army's intelligence division. Beginning with Metal Slug 2, the PF Squad also battles an alien threat to Earth (the Mars People), as well as several other supernatural threats including yetis, zombies, ambulatory Venus flytraps, giant crabs, and mummies. These outlandish elements were removed from the fifth game to return to the feel of the original title. The fifth moved to the motif of modern guerrilla warfare, leaving only traces of the series' signature quirky humor and paranormal enemies, with the exception of the final boss. Metal Slug 6 returned to the plot of the first three installments, bringing back Morden's Rebel Army and the Mars People. Metal Slug 7 has less outlandish elements with the Mars People replaced by an alternative universe of Morden's Army with futuristic equipment and weapons.