Once upon a time, the U.S. military needed to replace the Jeep. So it spent a brazillion dollars and came up with seriously capable off-road truck with the nickname-unfriendly acronymical sobriquet "HMMWV" made by AM General here in Indiana.
When compared to normal passenger vehicles, it was huge. Nearly a lane wide, with enough ground clearance to practically straddle a fireplug without dinging the oil pan, the HMMWV's mechanicals were shoved up into the truck to protect them from landmines, which resulted in a hood so high you needed Sherpas and oxygen to check the dipstick and a transmission tunnel that made a chat with your passenger a long-distance call.
Not only that, but it was positively agricultural in performance on pavement; it could be out-drag-raced by any minivan and its top speed necessitated drafting UPS trucks on the freeway to keep from getting rear-ended by diesel Rabbits.
It was terrifically butch-looking, however, and once Arnold Schwarzenegger showed up on the street with one, every Walter Mitty on God's green earth wanted one, too. At least until they found out what they were like up close. See, being a fairly specialized vehicle designed for the government, the price was nosebleed steep for 1992, and most folks willing to dump over fifty G's on a vehicle didn't want a slow one with an interior that could be cleaned out with a hose. Sales were, needless to say, as lethargic as the vehicle's highway performance.
General Motors bought the name "Hummer" from AM General in 1998 and decided to cash in on the popularity of the real military HMMWV by offering a more profitable vehicle. They took their existing pickup/SUV chassis and dropped a HMMWV-esque bodyshell on it and took the Walter Mitty market by storm with the new "Hummer H2" which was, essentially, a Chevy Suburban with a codpiece.
With the H2 selling well, GM slapped a chest toupee on their compact pickup and started selling it as the Hummer H3 and discontinued civilian sales of the actual HMMWV, which had been saddled with the moniker "Hummer H1".
This all occurred, of course, just in time for the price of gas to double and then, after a few more years, the economy to crater. Suddenly nobody wanted really big SUV's that cost a bajillion dollars, and that was bad news for a one-trick pony of a division like Hummer. Plus the government, which has just pumped oceans of money into GM, is threatening to raise the average fuel-economy requirement and mandate production of cars powered by moonbeams and unicorn farts, and when you take the king's shilling, you gotta dance to the king's tune. So it's adios Hummer; second baby out of the GM sleigh...