It was actually Sheila Michaels in the 1960s who initially started the push for it: https://en.wikipedia.org/wiki/Sheila_Michaels

Gloria Steinem cofounded Ms. Magazine in the early 70s which helped popularize it further.

Anyway, how old are you that well over half a century is “fairly new” to you? Do you still wear galoshes and use a mimeograph?