Lynn Conway. I didn't know about her until she passed away, but learning about her helped me gather courage to come out. She was also a pioneer in electrical engineering and computer science.
V.M. Glushkov. Soviet scientist who basically delineated cybernetics and computer science as a distinct field. He was about 50 years ahead of his time, so a lot of his best ideas we didnt really start fulfilling until quite recently. His grasp of the fundamental limitations of computers, and how to do useful things within them, was remarkable. He wasnt properly enabled and appreciated by the Soviets, so they were never able to lead the world in computing, but they had some impressive achievements. If you want to learn more, I recomend "Pioneers of Soviet Computing" and Glushkov's own "Introduction to Cybernetics". Of especial interest is his classification of algorithms and automata, nice to compare to modern programming paradigms and developments in new kinds of neural networks.
Ada Lovelace. She inspired me even as a young child. Just the idea that she could envision what the analytical engine would lead to solidly enough to become a programmer before there was a machine to program still thrills me.
Alan Turing. Pretty common choice, but sometimes when I get wistful about the world of technology, I wonder how things would have been different if Turing lived into the digital computer age.
His story is a warning for a modern age, where men and women can be tried and sentenced through surveillance without being guilty of a thing.
There are so many, but the first to come into mind was Knuth. The body of work is just insane for a one person (TAOCP, TeX/Metafont, literate programming/web, etc.).
