Ranma 1/2 was a Japanese fictitious martial arts gender-bending slapstick comedy comic book by Rumiko Takahashi, and had its heights during the 1990s. The protagonist, Ranma, is a martial arts boy who during travels in China fell into a cursed pond, which causes him to transform into a girl whenever he's splashed by cold water (hot water reverses the process).
The comic introduces several other martial arts characters, some of which has also fallen into similar ponds, transforming them into various animals.
The Ranma franchise was used for a whole lot of video games. When fighting games saw the light of day with Street Fighter II, it was only natural that the Ranma franchise was used for that genre too. As the US releases of these are pretty interesting, they deserve a special mention:
The first fighting game Chonai gekitou-hen (Neighbourhood Violent Battle chapter) was released in March 1992, after Street Fighter II arcade (june 1991), but preceding the SNES port (june 1992), boosting initial sales. However, Ranma 1/2 was not that a famous franchise abroad, and the US release of that game was graphically remade, and retitled Street Combat, released in 1993.
The second fighting game Bakuretsu rantou-hen (Explosive chaotic battle chapter) was released for Christmas 1992, and about one year later in the US under the title Ranma 1/2 Hard Battle.
The third fighting game Chogi ranbu-hen (Super skill chaotic fight chapter) was released in april 1994, and was scheduled for US release under the title Ranma 1/2 II Anything goes martial arts but was cancelled, probably due to bad sales of Hard Battle.
The Ranma gaming franchise also includes a fighting game for Game Boy (Netsuretsu kakutou-hen), several puzzle games and adventure games for teh PC Engine (Turbo Graphx) an RPG for the Super Famicon and finally, in 1996, a fighting game for Playstation (information from Japanese Wikipedia)