William Cowan was appointed to the position of Locomotive Superintendent of the Great North of Scotland Railway (GNSR) in 1857. Cowan is noted for introducing outside cylinder 4-4-0s to the GNSR. These gave greater boiler power over earlier types, but were sufficiently flexible for the GNSR's tight curves.

Cowan resigned from his post in 1883, to be succeeded by James Manson. Cowan moved on to become a steel tyre salesman for the German firm of Krupps, to both Britain and the US.