C was developed from a language called "B". B was developed from a language called "A".
Multics was the runtime OS that Unix was based on. The original versions of "Unix" - apparently a pun of sorts on "eunuch" and "Multics", or "castrated Multics", so to speak, ran on DEC PDP-11 architecture.
Unix was developed in response to a need for a more "programmer-friendly" OS; the command shells, process spawning and termination; the signalling and interrupt trapping; the lexicographic systems that arrived; the compiler compilers.
Unix was as open a system as its designers could make it. It became a standard because it was less restrictive, way more programmable; every configuration is available and editable as a text string in some file; a file can contain anything - structure is the user's concern, addressing file pages is the OS job; the graphical windowed interface design, which MS borrowed heavily from, was added on as a user-level system of interacting processes, all the parameters are of course, configurable as text.
Unix is a text-based paradigm like NT, and like VAX/VMS, except MS decided to hide a lot of it as binary-encoded, proprietary information.