Jim Shooter’s first published work in comics was writing and providing pencil breakdowns for Adventure Comics #346 (published in July 1966), featuring Superboy and the Legion of Super-Heroes.
He was just 13 years old when he wrote and drew the stories, and turned 14 shortly before publication. He submitted full scripts and rough layout breakdowns to editor Mort Weisinger, kickstarting a legendary career.
This is also the first Adventure Comics issue to feature a single, full-length comic story. It was called “One of Us is a Traitor!” This story is divided into two chapters. Shooter wrote both parts.
I don’t know if this should be a major or minor key. I am biased because I have been a huge Jim Shooter fan for 40 years. IMO, he is a legend in the comic community.