Sextus Empiricus is an important candidate I don't see discussed on LW. I don't endorse his positive philosophy, but his positive philosophy wasn't really what had the biggest influence; it was the distrust of speculation and theorizing he helped inspire. Historically, I wouldn't be surprised to learn that Sextus' demolition of all the theories of the day had a larger impact on the growth of science than any particular positive epistemological doctrine.

Anselm is another good candidate, surprisingly. He made philosophy cool again after the age of darkness, inadvertently planting seeds of intellectual investigation and disputation that would cause Christian thought to burn itself out. And scholasticism wasn't a thing yet, so he didn't even have much obfuscatory systematicity on his side to slow the rot.