Simons is right on both counts. Eugene the Jeep did grace a 1930s cartoon, "Popeye the Sailor," and was a cute little character who went around saying, "Jeep, Jeep!" in reply to anything said to him.
Simon is equally correct in his definition of the quarter-ton vehicle that the Army labeled a quarter-ton GP truck in 1940 (there is a famous picture of one climbing the steps to the Capitol).
The only added information I am able to offer comes from a knowledge of the times and the usual way of GIs to invent acronyms--nicknames--for just about everything.
GP simply had to become "Jeep!" It was a natural! What else could it possibly be called at a time when just about everybody followed the adventures of Popeye, Olive Oyl, Bluto and of course, the Jeep?
I know because I was there--living through the era as a serviceman hugely jealous of Jeep drivers and anyone lucky enough to ride in one. The discussion came up then, was answered the same way then, and surfaces again at intervals of around 10 years or so. Long enough for folks to forget Popeye and the "real" Jeep.
Some of the old cartoons still shown during the children's hours on Saturday and Sunday mornings occasionally resurrect Popeye and the Jeep, who still says, even in these troubled times, "Jeep, Jeep!"
JAMES N. BARDIN