Metal Slug was released in April 1996.
Etymology of 'Metal Slug': Meeher, the lead designer of the game for Nazca, wanted to create an armored fighting vehicle that could crawl on the ground like a 'slug'. The word 'metal' in the title indicates that the vehicle is mechanical. Initially, players considered the title to be "not good enough". Meeher later joked about the title, saying "Maybe I don't make much [sic] of a sense?"
Slugs in Metal Slug sequels included animals (usually only the Vulcan cannon mounted on the animal, with a cannon attachment occasionally available), planes and other vehicles that did not fit Meeher's original definition.
While being an obvious parody of World War II and the Nazi regime (the rebel army's flag is a deliberate pastiche of the Nazi "Swastika"), Metal Slug also lampoons 'Full Metal Jacket' and 'MASH'. General Morden, the rebel army's evil general, is a parody of Saddam Hussein.
Just as the two main heroes (Marco & Tarma) appear in every chapter in the Metal Slug series, General Morden & Allen O' Neill (the machine gun wielding, trash mouth-talking, buffed soldier) are the series' classic main villains.
The tank in Metal Slug was inspired by the tank: Dominio Tank Police (1988). The tank in this anime is called Bonaparte and is piloted by Leona Ozaki.
Cliff Reese holds the official record for this game with 2,683,030 points on March 8, 2011.
The same team that created Metal Slug had previously created a handful of games for Irem, most of which featured very similar graphics and gameplay. "Cyber Lip" (1990) had some of the core developers as the original Metal Slug. "Gunforce" (1991) and "In the Hunt
" (1993) had noticeably similar gameplay, with graphics that bear a slight resemblance to Metal Slug. "Gunforce 2" (1994) not only had similar gameplay but the sounds of dying soldiers were almost exactly the same as Metal Slug. Because of this, some fans refer to Gunforce 2 as "Metal Slug Zero".