In the late 80's, Atari Games created a subsidiary, Tengen, and became a Nintendo licensee. At the same time, they stole copyrighted information to get around Nintendo's lock-out chip. This led to the very first unlicensed games on the NES. A huge legal battle ensued that redefined fair use laws and Nintendo's 3rd party policies.
This video covers the history of Atari Games, the court case, and the aftermath