UNIX for Advanced & Expert Users

I've got a executable binary file (source code fortran77, compiled using gfortran).

I'm not sure this is even possible but I remember someone I knew was able to view the source code that created this binary file, i.e. he used a program that enabled him to see what the source code was.

Is this possible? If so what program could it be?

Thanks.

Linux I assume. objdump can show what the program is doing. There are decompilers
which produce assembler code (google for disassembler). In general most of these kinds of tools are not very useful, especially for compiled code -> Fortran source.

The problem with decompilers is that things like variable names, function names, class members, structure members, symbolic constants, and the like aren't preserved when source code is compiled into an executable; they all become offsets in memory or literal values. In decompilation, they just become generic names. Even the program structure may be altered by an optimizing compiler. This makes comprehending the structure and function of decompiled source code a mountain of detective work.