The December 2015 issue of Vital Speeches of the Day has the article, “The Man Who Made Winston Churchill,” by Hal Gordon, a professional speech writer. Originally delivered as a speech to the World Conference of Professional Speechwriters, the article describes the relationship between Churchill and Bourke Cockran, a politician who was known as America’s greatest living orator. The two met and became friends during Churchill’s trip to the United States and Cuba in 1895. Gordon considers Cockran and Churchill as speakers and includes Churchill’s quote when asked on whom had he based his oratory that ”It was an American statesman who inspired me and taught me how to use every note of the human voice like an organ. He was my model. I learned from him how to hold thousands in thrall.” The web site for Vital Speeches of the Day is available here.
A longer study of Cockran and Churchill’s friendship was published as Becoming Winston Churchill: The Untold Story of Young Winston and his American Mentor in 2007 by Michael McMenamin and Curt J. Zoller.