Ms. Pac-Man started its life as an unauthorized modification of Pac-Man by General Computer Corporation called Crazy Otto. Around the time GCC was creating Crazy Otto they were being sued by Atari over Super Missile Attack, an unauthorized modification they had made of Atari’s game Missile Command. GCC lost that case, and decided to try selling Crazy Otto to Midway, the company which had distributed Pac-Man in North America, rather than risking another lawsuit. Midway had been waiting impatiently for Namco to produce a sequel to Pac-Man, and they jumped on the chance to buy Crazy Otto. They modified the character sprites to make them look more Pac-Man-esque, making the main character female as a tribute to the female fans who helped make Pac-Man so popular.
The gameplay of Ms. Pac-Man is essentially the same as Pac-Man. The main differences are that the level color and layout change every other level, and the fruit bounce around the maze rather than remaining stationary.
Ms. Pac-Man was released in North America by Midway in 1981.