Diamond Reo was the final incarnation of a long line of vehicles manufactured in the United States.
The company had its foundation when Ransom Eli Olds left the automobile company he had founded over disagreements with financial backers. Unable to use his own name, he decided to use his initials for the new endeavor, thus creating the REO brand.
The first cars rolled out of his Lansing, Michigan plant in 1904. The REO brand soon surpassed the Olds brand in popularity.
In 1910 Ransom Olds purchased the property of agricultural implement maker Bemont and Sons, a business which had become defunct. The plant was reborn as a truck manufacturing facility to complement the line of automobiles already in production.
The Reo brand did well into the 1920s, then was challenged by economic conditions during the Great Depression. The company ended automobile production in 1936 while still continuing to produce trucks. The company survived and enjoyed new business by furnishing trucks for the war effort during WW II.
Despite its long history the company never regained the ground it had lost during the Great Depression. It struggled along until 1958 when it was purchased by White Trucks. White also purchased Diamond T, another truck maker who had fallen on hard times. It was hoped the merger would produce a stronger competitor, and the Diamond Reo nameplate was born.
The gamble was a failure. The last year Diamond T's were made under that name was 1967. In 1975 Diamond Reo filed bankruptcy and was sold to a southern investor, who in turn sold it to Osterlund, Inc. of Harrisburg, Pa. The company continued into the 1980s. Osterlund, Inc. sold out in 1993, a year which saw the formation of the new Diamond T Company.
Diamond Reo had become a niche manufacturer, excelling in the production of dump trucks and fire trucks as well as other specialized applications. They never enjoyed the widespread popularity of some of their competitors in the larger market of over-the-road highway trucks. Now the nameplate has become a footnote in history, an honorable mention in the long line of trucks no longer in production, an exhibit in truck museums.
Two bands have found their names from the venerable REO nameplate. Rock icon REO Speedwagon is named after one of the vehicles (a light delivery truck and precursor to the pick-up truck) produced in the company's earlier days. Country band Diamond Rio also bears the same name as the brand, though with a different spelling.
Sources:
http://answers.google.com/answers/threadview?id=85287
http://www.michigan.gov/hal/0,1607,7-160-15481_19271_19357-148239--,00.html
http://www.is-it-a-lemon.com/modules.php?name=News&file=print&sid=476
http://www.armyvehicles.dk/diamond.htm
http://www.antiquecar.com/index/listings/category963.htm#diamond_t