From a brief 4-issue Marvel comics series THE CAT issue 3 (1972-1973),
the first published letter of future comics artist Frank Miller, at age 16:








Most of you young'uns probably never heard of it. But the first issue has art by Marie Severin/Wally Wood and is a good story by a girl named Linda Fite (Herb Trimpe's girlfriend and later wife) with a somewhat feminist angle. The issues after have art by new talent at Marvel, including a final fill-in last issue with art by Jim Starlin and Al Weiss.

All 4 issues online where you can read them:

https://readcomiconline.to/Comic/The-Cat/Issue-1?id=89184#1


The character had a transformation (similar to the Beast in AMAZING ADVENTURES) into Tigra, and then another character took on the costume she wears in this series, and became a regular in THE AVENGERS during the Englehart, Shooter and Perez runs of the series (i.e., most of the 1970's and early 1980's).

Frank Miller started working professionally in comics in 1978, and within a year was a well-established talent on DAREDEVIL. I actually prefer Miller's earliest issues with Roger McKenzie writing (issues 158-167) to the ones after where Miller became writer/artist. But regardless, a remarkably fast jump from comics fan to comics pro.