James Black Discovers Propranolol

Having formulated a theory to annul the effects of adrenaline, he joined ICI Pharmaceuticals in 1958, remaining with the company until 1964, during which time he developed propranolol, which later became the world's best-selling drug. During this time Black pioneered a method of research whereby drug molecules were purposefully built instead of being synthesised first and then investigated for their potential medical uses. The discovery of propranolol was hailed as the greatest breakthrough in the treatment of heart disease since the discovery of digitalis.

http://en.wikipedia.org/wiki/James_W._Black