Its a story which dates back to a time when Xerox had an interoffice setup, using a GUI.
Both Apple and Bill Gates, went for the idea. I believe, but not sure, that Apple was the first to have what could be called a PC, with a GUI. I think Bill Gates actually bought the rights to use it ,Apple merely developed on what they had seen.
Microsoft was the first to actually give it a name "Windows". I suppose because he bult in programs popped up as windows, within the Windows OS
At the time, I was using a program with a windows/GUI interface, which was mounted on DOS. I think it was called Geoworks ,but I cannot track it down by googling. It worked very well, with a simple word processor, a paint program and a couple of other small things. I began to get more interested in the possibilities, some time around about Windows 2, as it was a complete OS, rather than a piggybacking program. It might well have been the first Windows, but I cannot put dates to it.