I think Stallman will argue that Open Source co-opted ideas from the Free Software movement. If that's true then you don't really have "Open Source" without Stallman's Free Software ideas.
But then I would also have to point out that software freedom isn't some great revelation that came to Dr. Stallman and started with him alone. Free software existed before the movement. Considering that, would you really have Stallman's idea of Free Software without what came before?
Maybe you would. But in any case I find it wrong to portray Stallman as the father of it all, let alone as the father of Open Source.
> “An article mentioned that I was the father of the open source software. I wrote back to the editor that if it were to be true, then the child that was conceived (open source) was a product of artificial insemination with sperms stolen from me without my knowledge and consent”. [0]
In any case, I don't think RMS would claim that he is the "father" of free software either, in the sense that he believes that software is inherently free. He may have been the father of a particular political movement (and organization) that advocates for this freedom, but saying that RMS "created" free software would be like saying that Martin Luther King, Jr.[1] "created" racial equality.
[0] Taken from http://linux4sanmukh.wordpress.com/2010/09/04/what-i-learnt-... , though he's been saying this in his talks for years