Inventor. Born in Keir (Dumfries and Galloway), the son of a blacksmith. Macmillan developed the first rear-wheel driven safety bicycle in 1842. This permitted the rider to power the bicycle by means of pedals attached to levers, which were attached to the rear wheel. Despite the effort required, the invention proved a success because the Hobby Horse, which was popular at the time, similarly provided momentum through the swinging of the riders's feet back and forth. However, Macmillan never patented his idea and it was therefore widely copied, although Macmillan was unconcerned.
He lies buried in the kirkyard at Keir and is remembered by a plaque on the smiddy in which he worked.