For when you need to transport people, go off-road, and pull big things.
The body-on-frame SUV has been reduced to basically six base vehicles in the US that have badge-engineered variants. As technology develops, automakers such as Land Rover are developing unibody platforms that are strong enough to build a large vehicle on, take the weight of a 4x4 drivetrain, and stand up to the rigors off-roading. That's an expensive proposition though and reflects in the cost to build as well as adding cost to the consumer while still having limitations.
The reason these vehicles have endured is because their underpinnings are so strong. A separate body being mounted onto a frame means that frame is less complicated to design, build, and modify. A well built frame will also allow more flex before something breaks when off-road and be strong enough to pull big loads anywhere. And, when you're talking about something for hard work and off-roading, there's a big advantage in being able to just unbolt a body panel and replace it.
There are big disadvantages to a body-on-frame design though. Bad fuel economy in the size of the engine needed to power the extra weight is very limiting now gas is more expensive. The higher centers of gravity have been mitigated somewhat by modern technology, but the on-road performance of body-on-frame SUVs is still lacking and not helped by the torsional flex available that helps the vehicles off-road.
While there are SUVs using purpose-built frame like the Jeep Wrangler and the Mercedes G-Class, they are in the minority. The vehicles in this list are the ones left that are descended directly from trucks and still soldier on in a sea of unibody blandness. They still hold the strength and off-road credentials that define them as true SUVs.
Ford's F-150 platform is proven and adaptable, and a no-brainer for Ford to use for its body-on-frame SUVS. Ford's Expedition and Lincoln Navigator have used the corresponding F-150 platform and shared some mechanical and body components for their production lives. The Expedition is also known as one of the longest-lasting vehicles on the roads with 5% of vehicles produced going over the 200,000-mile mark, which doesn't sound amazing until you consider the first model year for the Expedition was 1997.
The Navigator was the first Lincoln to offer seating for more than six people that wasn't a limousine. It also had true off-roading suspension with a live rear axle but came standard with the load-leveling air suspension that was an option on the Ford Expedition. The Lincoln has remained closely related to the expedition as its upmarket cousin. Recently, the Navigator in Black Label trim became the first Lincoln to cross the $100,000 mark.
The Land Cruiser is Toyota's longest running model. It started off as Toyota's answer to the question America answered with the original Jeep, but has grown into a modern 5-door full-size SUV. The current version debuted in 2007 and rolls on the same platform as the Lexus LX and a frame based on the second generation Tundra, and there's no sign of a redesign in sight.
The lineage of the Escalade is an interesting one. Cadillac wanted its first entry into the SUV market to go toe-to-toe with the Mercedes M-Class (now Mercedes GLE class). Initially, the Escalade was basically a 1999 GMC Yukon, which was a Chevrolet Tahoe that itself was built on the GMT400 truck platform used for Chevy's Silverado. Since then, and to this day, the Cadillac resides on a truck platform along with the Yukon, Tahoe, and Suburban SUVs.
When it comes to closely matched examples of badge engineering, the Tahoe and Yukon are brothers in arms while the Escalade is the svelte older sibling. Since it entered the market in 1991 the Tahoe, named after the rugged area surrounding Lake Tahoe in the Sierra Nevada Mountains, has regularly topped the best selling full-size SUV chart.
The Suburban is the longest running nameplate in automotive history, having been launched by GM in 1935. The Suburban as we know it now effectively started with the 7th generation and the 1973 model year under GMC.
Currently, we are on the 11th generation of Suburban and although it doesn't quite get the designation of iconic, it is one of the most easily recognizable SUVs out there. It's still used heavily today for duties with emergency departments including fire and EMS, as well as by government agencies including the FBI and Secret Service. Its most recognizable role is as an armored transport for the President of the United States for less formal engagements.
The original 4Runner was about as pure of a truck conversion you could get. It was basically a Toyota truck with a fiberglass cover over the bed. Since then, it has had a tight relationship with the Toyota truck and is still known as the Toyota Hilux Surf in Japan. The Lexus GX runs on the same platform, as did the now defunct FJ Cruiser.
The Lexus LX has only spanned three generations since 1996. The first generation was rushed through development due to looming trade sanctions threatened by the US on Japanese luxury vehicles. The first generation arrived with a straight-6 engine, and it wasn't until the second generation landed in 1998 that Lexus switched up to a V8 so it could compete properly with American full-size SUVs and the Range Rover as intended.
When the Armada first arrived it rode on the Titan truck platform for its first generation. Now, the Armada and Infiniti QX80 both roll on the F-Alpha platform that underpins Nissan's trucks, SUVs and the NV van. More specifically they use the Nissan Patrol variation, a vehicle that isn't sold here in North America but the nameplate goes all the way back to 1951.
Like the Land Cruiser, Toyota isn't in a rush to update the Sequoia. When it first launched, the Sequoia was directly aimed to compete with the Ford Explorer and Chevy's Tahoe. Currently, the Sequoia fills the gap between the 4Runner and Land Cruiser in Toyota's lineup here in the United States. The Sequoia is directly derived from Toyota's Tundra platform but the frame is fully boxed and the Sequoia uses fully independent and double wishbone rear suspension to improve the ride quality.