SD Gundam (Japanese: SDガンダム Hepburn: Esu Dhī Gandamu?, short for Superior defender Gundam) is a media franchise that spawned from the Gundam franchise. SD Gundam takes the mecha (and characters) from Gundam and expresses them in super deformed and anthropomorphic style.
SD Gundam originated from a contributed illustration of a junior student from Nagoya by the name of Koji Yokoi to the "Model News" magazine that Bandai was issuing in the 1980s. The illustration is of a Gundam but with an unusual proportion where the overall height of the Gundam is equal to twice that of its head. This illustration interested the chief editor and led to Koji Yokoi serializing SD Gundam in 4 frame comics in "Model News".
The super deformed designs were suitable for capsule toys, and so they were first merchandised as small SD Gundam-shaped erasers as part of the Gashapon series SD Gundam World in 1985. Built with a hole so they could be skewered into a pencil, the series was a hit with Japanese schoolchildren, and the concept soon expanded to other forms of merchandising and media, including models, manga, trading cards, anime and video games.
The popularity of SD Gundam was such that between the late '80s and early '90s, sales from the SD Gundam franchise far exceeded those of the rest of Gundam. And whereas Gundam pioneered the real robot branch of mecha anime, SD Gundam's more comical and exaggerated approach to the genre served to move it away from the ultra-realism that it was shifting towards in the '80s, and inspired a new flood of super-deformed robot shows the late '80s and early '90s such as Sunrise's Mashin Hero Wataru and Haō Taikei Ryū Knight, as well as video games such as the Super Robot Wars franchise.