Donald Hood Keefer was born in Highspire, Pennsylvania, on August 18, 1916. His parents, John E. Keefer, a butcher, and Edna Hood Keefer, had three sons; he was the youngest of those boys. When he was in his early twenties, Keefer moved to New York City, where he attended the American Academy of Dramatic Arts, graduating from that prestigious acting school in 1939. That same year, at the New York World's Fair, he performed various roles on stage in excerpts of works by William Shakespeare. During the 1940s, Keefer found work as supporting characters in Broadway plays such as Junior Miss and Othello. He also began studying method acting in Manhattan as an early member of The Actors Studio. In this period he gained some early experience as well performing in the new medium of television. In 1947 Keefer appeared in a televised presentation of Shakespeare's play Twelfth Night and in an episode of the anthology series Kraft Television Theatre. The next year he performed again on Kraft Theatre in an episode titled "The Silver Cord".