On a hiking trip in Alaska in 1920, Seattle resident Lloyd Nelson used a borrowed Indian pack to carry his gear. The pack was sealskin stretched over willow sticks, and proved to be uncomfortable to say the least. He thought he could design a better one, and thought there would be a market for one among boy scouts and outdoorsmen.
He designed a wooden frame that had a canvas panel stretched across it. The canvas rested the weight of the pack load on the user's back, keeping the wooden frame from gouging the user's back. He got a U.S. patent on the pack, which Eric Nicholson found out is U.S. Patent 1,505,661. Thanks, Eric!
He marketing the product by visiting every sporting goods store between San Diego and Seattle, and within a few years sales began to pick up. He sold his patent rights to Trager, the company making his canvas bags, and shortly after the sale, he got an order for 500 packs for the Forest Service, and another 500 unit order shortly followed.
By modern standards, the pack is cruel and unusual torture, but compared to the alternatives at the time, it was a big improvement.
My father-in-law carried a Trapper Nelson pack on a hike from the Hell's Canyon of the Snake River, to the town of Riggins, over the Seven Devils mountains. This was in the early forties, before WWII, and they carried canned food, an axe, a handgun, and other gear that made their pack weight extreme. I inherited his Trapper Nelson, which belongs in a museum now.