Harold Arminius Miller (December 9, 1875 – May 3, 1943), commonly called Harry, was an American race car designer and builder who was most active in the 1920s and 1930s.

Griffith Borgeson called him "the greatest creative figure in the history of the American racing car".

After a poor 1906 race season, Miller left for Los Angeles, California, to open a small machine shop specializing in carburetor production.

Tommy Milton supplied the financial backing to produce this engine but it was Jimmy Murphy who first won with it.

In the 1920s and 1930s, Miller engines also powered speedboats to several race wins and world water speed records.

With insufficient time available for their development and testing, all these cars dropped out when the steering boxes, installed too close to the exhaust, overheated and locked up.

Miller took some of the design elements from the Tucker Combat Car, notably the suspension, to American Bantam, where he was involved with the development of the first Jeep.