Answered Dec 12, 2017
Here’s another vote for:
Antonie Philips van Leeuwenhoek
He was an old-style scientist, who had a day-job, and just studied things because he was curious. If I am ever visiting an area where his original microscopes are on display, I will make a priority to check it out.
Other milestone-type people:
John Snow, who identified a public water pump in London as the source of a cholera outbreak, in 1854.
Robert Koch.
Louis Pasteur.
Alexander Fleming.