The Harley Davidson legend was born in 1901, with brothers William and Walter Harley and Arthur Davidson in Milwaukee, Wisconsin. Production began in 1903 when they built a grand total of three bikes, but these creations, made with borrowed tools and metal, were different from any other motorbikes at the time. They had a loop frame, a design that was unique to them, and were powered by a tiny three horsepower engine. By 1920 Harley Davidson had become the largest motorbike manufacturer in the world with dealers in 67 countries. In that year sales rose by a staggering 5000 percent.

The 'Knucklehead' engine was introduced in 1936 and the 1947 Harley Davidson EL 61 was the last bike to use it. The name was given to the engine by bikers who christened it Knucklehead because the valve covers looked like a fist with two knuckles. The engine was the first to use an oil circulation system, a vast improvement on the total loss system of previous models. The 1947 Harley Davidson had a new handshift four-speed transmission and a 'suicide clutch' which was operated by foot. It was the only civilian Harley Davidson OHV to use the straight leg frame until its re-introduction after the Second World War in 1954. The 1947 Harley Davidson with its wrap-around oil tank, rounded teardrop gas tank and many chrome accessories was a revelation in motorbike engineering.