Jobs was "inspired" by a visit at Xerox labs, they showed him a GUI built using Smalltalk (which they'd also invented). So naturally, he ran back to his office and invented GUI ;)
Or for third I guess lol Jobs demoed a mac gui to Gates, and apparently Gates ran strait to his Microsoft office, where he too invented gui. Jobs was very upset for years.
I think it actually was an Apple innovation, at least for {hobbyist, home, personal} computers. I did some digging and wasn't able to find anything before the Apple II+ in 1979. Please do prove me wrong, though!