who described many elements of the modern digital computer?

Answer 1

While von Neumann developed the modern concept of the stored program computer (especially the idea of program and data sharing the same memory), the invention of the computer is generally attiributed to Charles Babbage.

See http://en.wikipedia.org/wiki/Babbage

Answer 2

It was John von Neumann (1903-1957), he invented the idea of Memory, Aritmetic and Logic Unit, Central Processing Unit and Control Unit. All these elements exist in modern digital computer.