Robin Warren, the Australian hospital doctor who shared the Nobel Prize for medicine in 2005 for his work on the pathology of gastric ulcers. It appealed to me that someone based for far outside the big centers of learning could make such a big impact on science. Samuel Black was of a similar ilk: a physician in Newry, Co. Down from 1788 on, he began to report on cases that he encountered of angina pectoris, which had been first described in 1772, publishing details of 21 cases in all, 18 of which were accompanied by dissections that he conducted. He noted that clogging of the arteries - he called it "ossification" - was the visible feature that connected his patients, and predicted, correctly, that the "application of chemical principles" might permit the removal of these "deposits". (Others, including the English vaccination pioneer Edward Jenner, made similar observations independently of Black.) Black also became interested in the epedemiology of coronary disease, and was the first to comment on what became known, much later, as the "French paradox" - the fact that ischaemic heart disease - was comparatively rare in France. He believed that lifestyle, climate and stress conditions could explain this. There's a plaque commemorating Black over the Oxfam shop in Marcus Square, Newry, where he lived until his death in 1832.
Natural History Museum in London; her notebooks are at Myrtle Grove, near Youghal, the 16th century house built by Walter Raleigh in which she died in 1926.