A question suddenly occurred to me.
Mary Marvel, Billy Batson's long-lost twin sister, was basically a case, in the Golden Age, of "let's create an obvious female knockoff of a popular male superhero concept, and see how it goes!" I think she may have been the first such character to get to star in her own adventures. First as a feature within the pages of "Wow Comics," and later in her very own regular comic book series (with the catchy title of "Mary Marvel").
My question is: Were there any other female knockoff characters, in the Golden or Silver Ages, who also had that much success in the old days? Not just guest-starring in the adventures of the hero they were mimicking; not just appearing as the protagonist of a small feature within a larger anthology title; but making the big leap to being The Title Character of a brand new comic book series devoted exclusively to that young lady's solo adventures?
(Frankly, the next such example I can remember, off the top of my head, is Superman's cousin Kara Zor-El, who debuted as Supergirl in the late 1950s, but didn't get promoted to be the star of her own comic book series until the 1970s -- and I think her first regular title only lasted ten issues before DC pulled the plug.)
Anybody remember anyone else who went all the way from "female imitator of a popular male hero" to "star of her own regular title" before Kara Zor-El made that leap in the 1970s?