I think Al-Haytham (Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham) deserves at least a mention.
Many great names mentioned here, but Al Haytham surely has an impeccable claim. The great pioneer of the scientific method, ground-breaking work in several fields (optics, astronomy, mechanics), and pre-figured many of Newton's contributions to optics more than 600 years earlier.
And what sets him apart from the other great candidates mentioned here is that he did all of this more than 1000 years ago, before the enlightenment, before the renaissance, before the community of scientists in which the work of others blossomed. A truly remarkable man in the history of science.