December 14, 1989: Xerox Sues Apple

In exchange for the opportunity to invest one million dollars in Apple before the IPO, Xerox agreed to let a few of Apple's key players take a look at what the company was doing inside PARC.

Steve Jobs was, to say the least, enthused. So were the rest of the attendees. Upon returning to the Apple campus, they reinvented the Lisa project with a new direction in mind. Lisa came out and flopped, but the GUI lived on in the Mac.

It began to irk Xerox that Apple was raking in millions based on what Apple saw at its Palo Alto Research Campus. Nearly a decade after the Lisa was introduced, Apple's copyrights concerning the GUI of the Mac and Lisa were called into question when Xerox sued Apple on December 14, 1989.

Source: Apple Confidential 2.0, 80