Ford had the Bronco. Jeep had the CJ. Even International Harvester—the tractor company—had the Scout. And General Motors had…nothing?

Into that sport-utility vacuum, the Chevrolet K5 Blazer was born. With it, GM created a 4×4 that was both a direct response to the existing spectrum of SUVs and yet also apart from it. The key difference was size: Unlike its would-be rivals, the Blazer was based on the automaker’s successful full-size pickup truck. That cost-saving measure allowed it both to come to market quickly and to deliver greater capability than its competition.

Chevrolet was no stranger to the SUV world, having produced the Carryall/Suburban—a large, truck-based wagon—since the mid-1930s. Although offered with four-wheel drive, the Suburban didn’t have the same “Let’s go exploring” image that Ford’s and Jeep’s smaller fare did, and the Suburban consequently spoke to a different demographic.

In 1969, however, Chevrolet went all-out with the K5 Blazer to one-up its rivals in a bid to capture more youthful buyers. By basing the K5 on the existing short-box K10 pickup, Chevy offered two important advantages. First, the cabin offered acres of cargo space and interior room, made possible by its plus-size proportions. Second, the wider track and longer wheelbase smoothed its on-pavement ride.

In terms of styling and running gear, little differentiated the K5 Blazer from the pickups (or the now-three-door Suburban) of the same era, which had themselves been redesigned two years previously. There was one fairly big exception, of course: The first-generation Blazer featured a completely removable hardtop that left only the windshield sticking up from its soap-bar silhouette. A soft top was available with the truck, too, and base model Blazers initially didn’t even come with a roof or passenger accommodations. The driver had the only seat!

Mechanically, the K5 Blazer matched the pickup, with first-generation trucks offering both 250 (110 horsepower) and 292 (125 horsepower) cubic-inch straight-six engines as well as 307 (135 horsepower) and 350 (170 horsepower) cubic-inch small-block V-8s.

Three-speed automatics, an uncommon luxury in the SUV world at the time, or four-speed manual gearboxes performed shifting duties. The auto came with an NP-205 part-time four-wheel-drive transfer case, the manual offered a Dana 20 design. Rear-wheel-drive models were added to the lineup a couple years later and offered an independent front suspension. That added a bit more handling prowess to the topless Blazer’s wet-noodle chassis.

The Chevrolet K5 Blazer was an instant success, and it wasn’t long before the vehicle dominated SUV sales. GMC came out with their own version of the Blazer, the Jimmy, in 1970. Save for a few styling tweaks, the two models were essentially identical. Buyers instantly took to the combination of practicality, comfort, and style that the two sport-utilities offered.

That left Ford and Jeep scrambling to catch up and forced Dodge to hurry development of its own competitor, the Ramcharger, that would debut mid-decade. By the end of the first-generation Blazer’s production, yearly sales had increased by a phenomenal 10 times.

Changes were afoot for the K5 Blazer after only a few years of production, because the model was tied so closely to the development of Chevy’s full-size pickup. The new platform that debuted for both vehicles in 1973 was bigger, presented a slightly more rounded take on the “box” look, and offered much more daily comfort. It was also safer and stronger and featured a suspension that would carry the Blazer into the early ’90s.

For a brief period, 1973 to 1975, the Blazer occupied a “sweet spot” where it maintained the full-convertible design of the original model on the modernized drivetrain and chassis of the next-generation truck. For 1976, however, the K5’s removable roof transmogrified into a fiberglass shell above the rear passengers that could be unclipped and stowed in the garage with the front two occupants still safely ensconced underneath a full-cab roofline. This design change persisted for the rest of the Blazer’s production run.

Engine choices remained almost identical, although both sixes left by 1984, a 175 horsepower 400 cubic inch V-8 was offered until 1980, and GM briefly flirted with diesel from ’82 to ’87. Transmission choices expanded to eventually include a four-speed automatic while four-wheel drive systems would see a procession of continual updates, including a shift-on-the-fly system available for the entire ’80s. Dana axles disappeared from the picture entirely at the end of the ’70s in favor of GM’s 10- and 12-bolt corporate axles.

Initial customer response to the new, larger Blazer was positive to the point that Ford was forced to embiggen (yeah, what are you gonna do about it?) its own Bronco by swapping to a pickup platform. It wasn’t meant to last, however, and the 1979 energy crisis knocked K5 sales for a loop from which it never really recovered as Americans sought more efficient daily transportation—including the smaller S-10 Blazer, which debuted in 1983. With volume cut by nearly a third, the Blazer would bravely fight its way back by 1985 to nearly half of its late-’70s 90,000 unit-per-year glory.

By 1991, the all-new Tahoe waited in the wings and the thirst for two-door, full-size SUVs sat at a historic low. Not even the introduction of TBI fuel injection for the K5’s (now-standard) 210-horsepower 350 V-8 could make a difference.

Would there have been a big-body SUV revolution without the K5 Blazer? It’s hard to see Jeep leading the way with the good (but lower-volume) Grand Wagoneer and the Scout was never more than a blip on the sport-utility radar for mainstream buyers. Not even Ford had clued into the potential of pairing pickups and SUVs until a brand with as much clout as Chevrolet took a chance on blazing a trail with the K5. Markets change, and not all the pioneers who start the journey will be there at the end, but the K5 Blazer gave us a family-friendly, off-road ready tow vehicle for just over two decades. It helped usher in the era of the four-door full-sizers that eventually took over the game.