Why did Levi Strauss '?

Answer 1

He invented jeans, because he wanted to make pants that were comfortable to do heavy work in, but also heavy duty enough to withstand such work, and to do so cheaply using denim.

He didn't "invent" denim, but invented using brads to hold the seams together. Denim material had all ready been around for at least 400 years before Strauss. The crew of Columbus wore a type of denim. Strauss was working in the CA gold fields during the gold rush and because of the dirt and water his pants would wear out at the seams. He was a tailor by trade so he sat down and reinforced the seams with brads. Other miners saw what he had done wanted it too, so instead of making his fortune in gold he made it in denim.
Blue Jeans

He saw a need for pants that would stand up to the hard work in the gold fields and had a large supply of sail canvas.
While Levi did not invent blue jeans, his claim to fame was the invention of the metal rivet (that you find on the pockets, etc) that increased the durability of work pants.