Beck's Underground map (source: culturecatalysts.org)

Harry Beck (1902 – 1974), was an English engineering draftsman best known for creating the present London Underground Tube map in 1931.
Beck drew up the diagram in his spare time while working as an engineering draftsman at the London Underground Signals Office.
London Underground was initially sceptical of Beck’s radical proposal — it was an uncommissioned spare-time project, and it was tentatively introduced to the public in a small pamphlet in 1933. It immediately became popular, and the Underground has used topological maps to illustrate the network ever since.

Source: Wikipedia