Louis Hervé Coatalen (11 September 1879 – 23 May 1962) was a Breton automobile engineer.
After working for De Dion-Bouton, Clément-Bayard and Panhard-Levassor he left France to work in England in 1900. After a short time with the Crowden Motor Car Company he became chief engineer with the Humber Car Company in 1901.
In 1906 he went into partnership with William Hillman to form the Hillman-Coatalen company. The partnership was dissolved in 1909 when Coatalen moved from Coventry to Wolverhampton to join Sunbeam, becoming joint managing director in 1914.
During World War I he designed aircraft engines for Sunbeam.
In 1920 Sunbeam joined with Talbot and Darracq to form STD Motors Ltd and Coatalen had a seat on the board as one of the directors, remaining chief engineer of Sunbeam. His main interest became racing cars and Sunbeam became heavily involved in land speed record attempts including the successful 1000HP car of 1927 and the failed 'Silver Bullet' of 1930. This catapulted Sunbeam to the highest echelons of international competition from the legendary success at the 1912 Coupe de l’Auto to winning the 1914 and 1922 Tourist Trophy and 1923 and 1924 Grand Prix. Coatelen collaborated with the industry foremost designer Ernest Henry on the 1922 Grand Prix Sunbeams and had some of the most respected drivers of the period – Henry Segrave, Jean Chassagne and K L Guinness driving his cars.
In 1926 Sunbeam's racing activities were taken into the STD company and moved to Suresnes in France and although Coatalen continued working part-time in Wolverhampton, he spent most of his time in Paris. STD failed in 1931 but its affairs were so complex it took until 1934 to sell the Suresnes works to Lago.
During World War II he lived in France, although he had earlier taken out British citizenship, and he continued living there until his death.
Louis Coatalen married four times: in 1902 to Annie Ellen Davis (divorced 1906), in 1910 to Olive Bath (daughter of a Sunbeam director), in 1923 to Iris van Raalte, née Graham, and in 1934 to Ellen Bridson. Known to family as Dickie.