Book and Regular – who started?

Matthijs Sluiter
Matthijs Sluiter Posts: 14
edited December 2020 in History of Typography
When did the habit/feature com about of having both Book and Regular in a typeface?
And if anyone knows, was this around the same time for Sans and Serif? 
Was this introduced by multiple foundries?
So many questions.
Today I thought I knew something about this subject, but on second thought I have no clue what my assumptions are based on.

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