Brother of Monty, early race driver. Mortimer was a mechanic with the Stevens company. Of Welsh ancestry (his father was an engineer from Wales who moved to the US in the 1870's), he was mainly based in New Jersey and also worked for Hudson and away from the sport, he worked in a glassworks. Mortimer took up racing in 1910. Mortimer's crowning achievement was winning the Pabst Blue Ribbon Trophy in 1912. Roberts served in the US Army during World War 1 and also served as a volunteer veteran during the Second World War despite being over 50 years of age.

Biography last updated 13 Feb 2016