Manga creator Rumiko Takahashi derived Ranma's name from the Japanese expression "kaitô ranma" which means "solving a problem swiftly and skillfully". She based it from that phrase because she was having difficulty thinking up a name for him.
Rumiko Takahashi was originally going to have the characters "change" whenever they were hit or punched, but changed it to hot/cold water when she realized the characters would change every few seconds during a fight scene.
The character of Ranma and the initial inspiration for the entire series originally spawned from Ryuunosuke Fujinami, a secondary character in Rumiko Takahashi's previous work "Urusei Yatsura" (1981). Ryuunosuke is a girl raised by her maniacal, single father to be a boy, and became skilled in martial arts through his daily, brutal training. She constantly longs to express her pent-up feminine side, but obstacles (usually her father) keep getting in her way.