I'd also suggest that cellular automata are now an important area of theoretical Comp Sci (and a number of related fields). Wolfram's contribution in that area

I'd also suggest that cellular automata are now an important area of theoretical Comp Sci (and a number of related fields). Wolfram's contribution in that area compares quite favorably with the pioneering work by Von Neumann and Conway, providing a lot of the foundation for systematic study of those types of system.