For starters? Him because he is 'the father' of the *BSD filesystems:
https://en.wikipedia.org/wiki/Marshall_Kirk_McKusick
That's all online via the web, as PDF, annotated and whatnot.
For 'something else': https://en.wikipedia.org/wiki/Be_File_System
As living on via Haiku, and documented there under 'Other Resources':
https://www.haiku-os.org/documents/
