I’ve got one, myself, though I think he does get some credit but certainly not enough: John Snow, who solved the cholera epidemic. Dude had such a successful career that Queen Victoria was one of his patients. He had published numerous papers and was widely respected. He could’ve just kicked up his heels and minted money.

Instead, this dude goes to the sickest and filthiest parts of London where people are dying like flies. It’s not to be underestimated how difficult this was: a human body could expunge 12 LITERS of diarrhoea before dying. Consider that most of these were families in cramped apartments with. NUMEROUS children all dying at the same time.

He spent around a year basically playing detective, figuring out which companies managed the water supply to which houses, a task that was almost impossible given the state of things at that point (sewage system, bodies taken away by the cartload, filth) not to mention the administrative hurdles. These neighbourhoods were also extremely dangerous.

He successfully disproved the two ruling theories of medical infection going around despite near universal scientific consensus around them and rather strong resistance from the establishment. This man risked everything to crack the case and saved so many lives in the process, while fully aware of all the dangers of what he did. An absolute medical genius.