“Jeep” was a vehicle born out of necessity, and developed in just seven weeks to meet the needs of the U.S. Army that was looking for a small, all-terrain lightweight vehicle with four-wheel-drive, able to go anywhere, delivering troops, supplies or serving as a weapons platform. Jeep was also expected to be compact, lightweight, relatively powerful, incredibly durable, and capable of carrying heavy supplies and munitions. In other words, they wanted someone to pull off an engineering miracle.
The Willys-Overland Motor Company, whose MB prototype ultimately won the contract from the Army. Almost immediately, the demand for the Willys MB was so great that they had to get the help of Ford just to keep up with the military’s needs. On 1st August 1941, the first ‘Jeep‘ was produced.
Not surprisingly, the Willys MB was an instant hit with the troops. They affectionately nicknamed it after Eugene the Jeep, a mysterious animal in the popular Popeye comic strip that could walk on walls and seemingly teleport from one place to another. As far as soldiers were concerned, their 4x4 Jeeps could do the same thing.
The Jeep became the primary light 4-wheel-drive vehicle of the United States Armed Forces and the Allies during World War II, as well as the postwar period. The term became common worldwide in the wake of the war.
In lowercase, the term "jeep" continues to be used as a generic term for vehicles inspired by the Jeep that are suitable for use on rough terrain. In Iceland, the word Jeppi (derived from Jeep) has been used since WWII and is still used for any type of SUV.
According to Wikipedia & carthrottle.com