William Walmsley (born 1892) was with William Lyons a co-founder of the Swallow Sidecar Company, which later became the Jaguar car company.
Walmsley was born in Stockport, England, the son of a coal merchant. When his father retired in 1921, the family moved to Blackpool. Walmsley then lived in King Edward Avenue, close to William Lyons. Walmsley had designed a motorcycle sidecar which attracted Lyons, who bought one. The following year, the men decided to begin producing the sidecar commercially. The Swallow Sidecar Company of Blackpool was the result.
In 1927, the company started coach-building motorcars, putting their own bodywork on an Austin Seven chassis. Four years later, they contracted to buy engines and chassis from Standard Motor Company. Sales were good, and at the 1931 London Motor Show their SS class car was exhibited. It cost under £350.
Walmsley had a personal 1934 SS.1 two seater commissioned.
Walmsley was content with the company's modest success and saw little point in taking risks by expanding the firm. Lyons bought him out and became the sole owner in 1935, shortly after the company had moved to Coventry. Walmsley continued in business making trailers.
The name "Jaguar" appeared as "SS Jaguar" in 1935 after Walmsley had left the company and later after World War II the company was renamed as Jaguar Cars to avoid unfavourable connotations of the SS initials of the Nazi Party.