This is one of my answers compared previously on Quora.
Since the question does not specify if it is about computer scientists that are still alice or not I will bring here my favorites.
Probably the best of them was that brillian mind of Alan Turing. Is the “Turing Machine” which gave the foundations for today computing machines we use for writing on Steemit. His contribution was essential in solving the Enigma code nazis used for coding their radio communications during WWII.
In the same time more or less there was also Akira Nakajima and Claude Shannon wich contributed further on switching circuits theory at the basis of our transistor based computers.
Another great scientist was John von Neumann also called the father of modern computer’s architecture.
From the 50′ to our days there were many other scientist that I cant recall or I dont even know about.
However regarding the last years I can mention Edsger W Dijstra, Andrew Ng, Luca Trevisan, Gary Miller and many others.