William Cudmore McCullagh Lewis, FRS (29 June 1885 – 11 February 1956) was a British chemist and academic.
He was born in Belfast, the son of linen merchant Edward Lewis and his wife Francis Welsh McCullagh.
After gaining an MA degree in 1906, he was a demonstrator for a year and then moved to England to do research in physical chemistry at the University of Liverpool.
A similar theory was also propounded by Max Trautz in Germany in 1916, unbeknown to Lewis because of the first World War.
He had married Jeannie Waterson Darrock, with whom he had one child, Ian, who became a physicist at Harwell Atomic Energy Research Establishment.