Ralph Roscoe Proctor was an American Civil Engineer well-known as the inventor of the 'Proctor test' and the associated theory of compaction.

As a veteran of World War 1 who served the Company E, Twenty-Third Engineers, he was primarily involved in railroad construction work in France. Afterwards, having completed his studies in Civil Engineering at the University of Southern California in Los Angeles (1914-1916), Ralph Proctor worked at the California Water Authority of Los Angeles (BWWS - Bureau of Water Works and Supply), where he remained during the rest of his career, mostly involved in construction, design and maintenance. Much of his field experience was diverse in water resources, geo-hydraulics and in-situ foundation works (Grundbauaufgaben), but his efforts were particularly focused in dam construction. He played a key role in the construction of St. Francis Dam and was also involved in the investigation of its failure. During the construction of Bouquet Canyon Dam (1932 to 1934), he developed what we now call the "Proctor-test", to determine the optimum water content of the compacted earthfill used for the dam core construction, ensuring both stability and the desired permeability of the compacted fill. He established quantitatively, that for a fixed compression energy imparted to a given soil sample at a known water content, the achievable density would be unique, such that the maximum dry density was attained at the optimum water content. He published these results in 1933 which helped to revolutionise the construction of highways, railroads and airport runways, apart from dams (adapted from Wikipedia and ASCE Transactions, Vol. 128, 1963).