William DeWolf Hopper was an American actor, singer, comedian, and theatrical producer. A star of vaudeville and musical theater, he became best known for performing the popular baseball poem "Casey at the Bat".

"Casey at the Bat: A Ballad of the Republic, Sung in the Year 1888" is a mock-heroic poem written in 1888 by Ernest Thayer. It was first published anonymously in The San Francisco Examiner on June 3, 1888, under the pen name "Phin", based on Thayer's college nickname, "Phinney". Featuring a dramatic narrative about a baseball game, the poem was later popularized by DeWolf Hopper in many vaudeville performances. It has become one of the best-known poems in American literature.