R. J. Mitchell, English engineer, designed the Supermarine Spitfire and Supermarine S.6B (d. 1937)
Reginald Joseph Mitchell CBE, FRAeS, (20 May 1895 – 11 June 1937) was a British aircraft designer who worked for the Southampton aviation company Supermarine from c.1917 to 1936. He is best remembered for designing racing seaplanes such as the Supermarine S.6B, and the Supermarine Spitfire.

Born in Butt Lane, Staffordshire, Mitchell attended Hanley High School and afterwards worked as an apprentice at a locomotive engineering works, whilst also studying engineering and mathematics at night. In 1917 he joined Supermarine, where he was appointed Chief Engineer in 1920 and Technical Director in 1927. Between 1920 and 1936 he designed 24 aircraft, which included flying boats and racing seaplanes, light aircraft, fighters, and bombers. From 1925 to 1929 he worked on a series of racing seaplanes, built by Supermarine to compete in the Schneider Trophy competition, the final entry in the series being the Supermarine S.6B. The S.6B won the trophy in 1931, and that year he was awarded the CBE. When in 1931 the Air Ministry issued specifications for a new fighter aircraft, Supermarine submitted Mitchell's design, the Type 224, but this was rejected by the RAF. Mitchell was then authorised by Supermarine to proceed with a new design, the Type 300, which went on to become the Spitfire.

In 1933, he underwent surgery to treat rectal cancer. He continued to work and earned his pilot's licence in 1934, but in early 1937, he was forced by a recurrence of the cancer to give up work. After his death that year, he was succeeded as Chief Designer at Supermarine by Joseph Smith.