Of the non-government agency guesses, this one would be the most credible if not for one thing - not even Szabo could sit on $50 Billion in bitcoin and just casually never spend it. The NSA is the most credible culprit as Bitcoin creator.

However, I do think Nick Szabo is the mysterious "Nicolas van Saberhagen" creator of Monero. Besides, Monero aligns more with his ideology. Bitcoin is supremely traceable and a handy tool for government. Monero, not so much.