Perl started with Henry Spenser's regular expression library, which was written in the mid-1980s. That got used in a lot of places, and may have been used in sed. It includes backreferences. I don't know what predates that.

Perl used that as a starting place and began adding extensions such as the difference between .* and .*?.

So using "non-regular thing" as a regular expression predates Perl. But the dialect we standardized on with the features people now expect is due to Perl's influence.

Ah I get you.

I've tried finding some source for early versions but all the links I've found are dead. It's an interesting question!