In 1839, a Scottish inventor named Kirkpatrick Macmillan created a product which helps people get from point A to point B. Millions of this product have been sold. What was it?

While two-wheeled "walking machines" existed before the 1830s, they required riders to push off the ground with their feet, much like a modern balance bike. Scottish blacksmith Kirkpatrick Macmillan is credited with a revolutionary leap forward around 1839 by creating the first mechanically propelled two-wheeled vehicle. He ingeniously added a system of pedals on levers, which were connected by rods to the rear wheel. This allowed a rider to propel the machine forward without their feet ever touching the ground, establishing the fundamental concept of the modern bicycle.

Macmillan's machine was a heavy contraption with a wooden frame and iron-rimmed wheels, but its rear-wheel drive concept was groundbreaking. Although some historical debate exists regarding the definitive proof of his invention, his design is widely recognized as the crucial link between the earlier foot-pushed hobby-horses and the pedal-powered velocipedes that would follow. This single innovation paved the way for the cycling craze of the late 19th century and the millions of bikes that have provided transportation and recreation ever since.