https://en.wikipedia.org/wiki/Bertrand_Serlet https://en.wikipedia.org/wiki/Avie_Tevanian

Bertrand wrote malloc, top, and quite a bit of code at NeXT.

Avie wrote Mac Missles! in the 80s: https://www.youtube.com/watch?v=Ir8H0NuPZRU

... and, well, Mach:

   http://www.cs.ubc.ca/~norm/508/2009W1/mach_usenix86.pdf
   ftp://ftp.cs.cmu.edu/project/mach/doc/unpublished/exception.ps
   ... etc etc.

Steve Jobs relied on extremely technically capable management that didn't just hand off understanding to their staff.