Ernest Lawrence Thayer (August 14, 1863 - August 21, 1940) was an American writer and poet who wrote "Casey at the Bat".

Thayer was born in Lawrence, Massachusetts and raised in Worcester. He graduated magna cum laude in philosophy from Harvard in 1885, where he was editor of the Harvard Lampoon. Its business manager, William Randolph Hearst, hired Thayer as humor columnist for the San Francisco Examiner 1886-88.

Thayer’s last piece, dated June 3, 1888, was a ballad entitled "Casey" ("Casey at the Bat").