Surprised nobody has mentioned any/all of Alan Turing's work, it is the mathematics which caused the foundation of Computer Science. See Turing Completeness and

Surprised nobody has mentioned any/all of Alan Turing's work, it is the mathematics which caused the foundation of Computer Science. See Turing Completeness and Universal Turing Machines. Graph Theory is important for understanding data structures, I would also stress that the math equivalence of idempotency and isomorphism. We use these concepts a LOT in our work - but admittedly, we're a database ( http://gun.js.org/ http://gun.js.org/ ), which is a very different line of work than building consumer apps. Other people already mentioned Big-O notation. Combinatorics, etc.