Did William Shakespeare exist?

[Aegon]

It's that his historicity is "unquestionable doctrine" that raises issues.

...and that's irrelevant. Historians aren't theologians. The people researching this, for the most part, aren't out to prove Christianity. They research to find out whether or not a guy named Jesus existed at that time and was known as some sort of prophet figure. That's it. His historicity. If people want to say "He existed and if you don't think so you're a blasphemer and you should die at the stake" that's a separate problem and, again, irrelevant to whether he really existed or not.