Claude C. Hopkins
Claude C. Hopkins (1866–1932) was one of the great advertising pioneers. He believed advertising existed only to sell something and should be measured and justified by the results it produced.
He worked for various advertisers, including Bissell Carpet Sweeper Company, Swift & Company and Dr. Shoop's patent medicine company. At the age of 41, he was hired by Albert Lasker owner of Lord & Thomas advertising in 1907 at a salary of $185,000 a year, Hopkins insisted copywriters research their clients' products and produce "reason-why" copy. He believed that a good product was often its own best salesperson, and as such he was a great believer in sampling.
To track the results of his advertising, he used key coded coupons and then tested headlines, offers and propositions against one another. He used the analysis of these measurements to continually improve his ad results, driving responses and the cost effectiveness of his clients' advertising spend.
His classic book, "Scientific Advertising," was published in 1923, following his retirement from Lord & Thomas, where he finished his career as president and chairman. He died in 1932. Charles Duhigg credits Hopkins with popularizing tooth brushing, as a result of Hopkins' campaigns for Pepsodent. 
A short movie on the book Scientific Advertising - Claude Hopkins can be found on http://www.youtube.com/watch?v=6copAh_SDCU&feature=youtu.be.This book was followed, in 1927, by his autobiographical work, "My Life in Advertising."
- Scientific Advertising Free Online Copy - All 21 Chapters & author photo
- Season Five. "All Things Being Equal: The Fascinating World of Parity Products" host Terry O'Reilly focuses on Claude Hopkins
- Dughill, Charles. The Power of Habit: Why We Do What We Do in Life and Business. Random House.