Branding the Presidents of the United States
Twenty-Ninth President: Warren G. Harding (1921-1923)
Harding was the first president to be heard on the radio. 

“President Warren G. Harding, while addressing a crowd at the dedication of a memorial site for the composer of the “Star Spangled Banner,” Francis Scott Key, becomes the first president to have his voice transmitted by radio. The broadcast heralded a revolutionary shift in how presidents addressed the American public.”
-americanhistory.com