Robert Arthur "Robin" Riddles, CBE, MIMechE, MinstLE (23 May 1892 – 18 June 1983) was a British locomotive design engineer.
Riddles entered the Crewe Works of the London and North Western Railway as a premium apprentice in 1909, completing his apprenticeship in 1913.
When work on that was stopped, Riddles was placed in charge of a small production progress department and was sent to Horwich to study the methods used by the L&Y.
On the death of Charles Fairburn in 1944, he applied for the position of Chief Mechanical Engineer, but the job went to George Ivatt, with Riddles being promoted to vice-president of the LMS.
The duties of the three effectively covered the old post of Chief Mechanical Engineer and they subsequently oversaw the design of the British Railways (BR) standard classes.