In 1937, Fred Avery introduced a new character in his cartoon short Egghead Rides Again. Egghead was initially depicted as having a bulbous nose, funny/eccentric clothing and a bald, egg-shaped head. Many cartoon historians believe that Egghead evolved into Elmer over a period of years, including animation historian Michael Barrier who asserts "The Egghead-Elmer story is actually a little messy, my sense being that most of the people involved, whether they were making the films or publicizing them, not only had trouble telling the characters apart but had no idea why they should bother trying."

The story begins with Duck Dodgers (Daffy) being tasked with locating the uncharted "Planet X", the only remaining source of the dwindling element Illudium Phosdex, a.k.a. "the shaving cream atom".

His head is a black sphere with only eyes for features.

He usually wears a yellow sombrero, white shirt and trousers (which was a common traditional outfit worn by men and boys of rural Mexican villages), and a red kerchief, similar to that of some traditional Mexican attires.

Rabbit is the missing ingredient, and unfortunately for Bugs, he is the nearest rabbit.