Actually, the whole point of developing C was to write Unix in it! Early operating systems were written in assembly language, which meant they needed to write a new OS for each new mainframe design. The idea of Unix was that if you wrote the OS in a high-level language, you'd just need to write a new compiler for each new computer. But what language? Hardly Fortran. They looked at developing BCPL but eventually gave up on it. They'd been referring to that as B, so they called the new language C. Incidentally, the reason why Unix has the X window system is that the prototype had been called (what else?) W.

Unix®, Linux®, Posix®, AIX®, and GNU® are all registered trademarks in the United States. And they all refer to different things.

(So, when people refer to "GNU Linux," they are actually abusing two registered trademarks having two different owners! Legally speaking, you can't do that.)

As some very expensive lawyers discovered in a long legal defeat documented at groklaw.net, Linux® is an entirely original operating system which shares no source-code with Unix® but which re-implements (and, improves upon) much of its API and operating concepts. Of course, Linux® today has gone much beyond its original inspirations, as has Unix.® The teams responsible for both products are of course very aware of one another and cooperate closely on many things, although their efforts diverge in some areas.