[TUHS] Why do compress(1) and pack(1) use the .Z / .z extension?

[Hans Wennborg]

I'm trying to find out why compress(1) uses .Z as filename extension.

My theory is that it was inspired by pack(1), which uses the .z extension.

However, I haven't been able to find any info on why pack(1) uses that 
extension. Does anyone here know?

Some searching led me to [1] which is a man page for pack from AUSAM. 
It's written by Steve Zucker in 1975, so perhaps the extension is z for 
Zucker?

Was Zucker's pack(1) the first, though? This message [2] talks about a 
Bell version.

Does anyone here have any information about this?

Cheers,
Hans

1. https://minnie.tuhs.org/cgi-bin/utree.pl?file=AUSAM/doc/man/man1/pack.1
2. https://tech-insider.org/unix/research/1984/0319.html