Origin: 1935–40, Americanism; alteration of G.P. (for General Purpose) Vehicle, or special use of Eugene the Jeep, name of fabulous animal in comic strip “Popeye” by E. C. Segar
1941, Amer.Eng. military slang, from G.P. "general purpose (car)," but influenced by Eugene the Jeep (who had extraordinary powers but only said "jeep"), from E.C. Segar's comic strip "Thimble Theater" (also home of Popeye the Sailor). Eugene the Jeep first appeared in the strip March 13, 1936.