Quoting admiralWillyWilber,
Unix right Jack. Not to mention that he did this in assembly language one of two native languages the computer speaks. He didn't even have a high level language to work with for this in the beginning. Linix is the free version of this. You must of been happy when C came out.
The OS is one you may not have heard of. As of my retirement it was called MVS, although it had had many name changes before then, and in its earlier incarnations predated Unix. We also had VM as an operating system, which had some special purposes.
As to higher level languages, PL/1 came out in the 1960s, FORTRAN came out in the 1950s, and COBOL came out in 1960-1961. All three of these Generation 3 languages predate the arrival of C. We also had a series of Gen 3 compilers that were internal to the company.
They talked about languages in generations, kind of an easy way of saying how many levels away from machine code the language was, Generation 1 was machine code (not even an assembler), Gen 2 was assembler, Gen 3 was higher languages, including both compiled and interpreted languages. There was talk of Gen 4 languages, but I never saw a language that ever lived up to the billing. If you are interested, you can look up these languages in Wikipedia. When looking for C, you may have to look for "C (programming language)". Other languages you may be interested are "ADA (programming language)", PASCAL, "Basic (programming language)", and REXX. Basic and Rexx are older examples of interpretive languages (interpreted and run at time of use). All of the others mentioned above are compiled languages (compiled into machine language code before use).
If you are interested in other trivia, HTML, XHTML, and CSS are, in appearance at least, outgrowths of a set of document compilers called "Document Composition Facility" languages, one of which was called SCRIPT ("Script (markup)" in Wikipedia). There are many outgrowths of these now.
JAVA and JAVAScript fits in here somewhere, but I think we have been off topic enough as it is.