jimmy olsen

The origins of Jimmy Olsen are a little murky.  Almost from the beginning the Daily Star had a bow tied inquisitive office boy that helped Lois get into trouble.  From Action Comics 6 by Jerry Siegel and Joe Shuster November 1938
In April 1940, a young boy got tangled up with criminals trying to protect his mother's store from gangsters.  Superman secretly came to the aid of young Jimmy Olsen (played by Jackie Kelk) and Clark and Lois got him a job at the Daily Planet afterwards.  Producer Robert Maxwell probably named him after a pulp writer who used to sell stories to Harry Donnefeld's pulp magazine line.
It was logical therefore for the office boy to become Jimmy Olsen, which he did in Superman 13 in a story by Jerry Siegel and Leo Nowak. November 1941
Jimmy didn't actually get a last name until 2 issues later.  Superman 15 by Jerry Siegel and Leo Nowak.