@jkl Yeah you are right, but still, that Unix was written (mostly) in C and maybe more important being compiled with the C compiler, making it very much more portable then any other OS prior. Is very important to how Unix was designed, and developed.
This interview with Brian Kernighan, is probably the source of where my first statements came from (also confirming jkl s corrections):
https://www.youtube.com/watch?v=de2Hsvxaf8M

I think that understanding the environment (Bell Labs), where Unix (and C) was developed, is good to know to "understand" Unix (I barely know what it is myself, and i have read many books and binged similar youtube clips for years..). Especially for people not from the US, i guess that AT&T and Bell Labs is common knowledge in US, but few know about it in the rest of the world (those who know probably have a good understanding of Unix already).

I would also try to explain the principles of "pipes" , which also is something that have shaped unix a lot.