Microsoft didn't create or invent any DOS. They bought it for about 50 grand and went into licensing with IBM. Up to version 6.1, PC DOS was just MS DOS rebranded. After 6.1, PC DOS was only an IBM product. Many still consider DOS to have been at best "inspired" and at worst ripped off from CP/M. Ironically, the creator of CP/M ended up later working for Microsoft.
My only chortle was when Bill Gates publicly stated that OS/2 will be the greatest operating system yet. Admittedly, though not an Apple user then, I was very excited about the "Pink" project that didn't get beyond the drawing board.