Xerox created the Alto, the first computer with a graphical user interface (GUI). According to legend, and possibly even fact, Steve Jobs and Apple engineers visited Xerox, liked the idea and decided to use it for the Macintosh. Gates saw the Macintosh and created Windows, more graphically based than MS-DOS was. (I always liked MS-DOS. Yes, it helped to memorize commands. But even so.)

So Xerox invented the idea, Apple copied it, and Windows copied Apple. At least that's the story I've heard.