Brief highlights of scientists who do/did cool stuff. I'm gonna try to do them roughly 2x/week. Feel free to add your own if you want! Warning: may be biased towards biologists.
Carl Woese Woese is super famous in microbiology circles and maybe biology in general, but I don't know if he's at all known outside of those. His most famous work involved analysis of the 16S gene in prokaryotes in the late 70's. Using DNA sequences, he showed that prokaryotic microbes weren't all bacteria, but that there are actually two groups: one made up of organisms traditionally considered bacteria, and one of smiliar but distinct organisms that seemed to be most abundant in extreme environments: archaea. This was a huge deal: we went from a two-domain system (prokaryotes and eukaryotes) to a three-domain one composed of Eubacteria, Archaea, and Eucarya. This was rejected until about the mid-80s, and today most people are on board with this split of the prokaryotes into two groups. Further research has suggested that archaea are more closely related to the rest of the eukaryotes than bacteria are, so we may have descended from an archaea-like ancestor! Also, archaea aren't just the extreme environments organisms that people originally believed: they also seem to be present, if not abundant, in many environments. Moreover, 16S sequencing became the "gold standard" for microbiological classification, although more recently other standards are being developed because 16S doesn't work equally well for categorizing all microbial lineages. However, 16S has been instrumental for enabling sequence analysis of microbes and revealing the incredible diversity of microbial life. There he is, ca. 2004.
