Well, the father of sola fide is Marcion. Some Baptist and reformed individuals see him as the start of the "alternative" church. In my opinion they couldn't have picked a better individual. :)
OK, so we started with baby steps at the beginning. :) One thing I read about Marcion was that all of his actual writings have been lost, so everything we know about him is only through his critics. Even so, from what I read it looked like there were plenty of ideas I would disagree with. I don't think we can be sure how many of them he actually held. In any event, it is one small piece of evidence that Luther did not simply make up what he wrote out of whole cloth.