Del Close (March 9, 1936 - March 4, 1999 ), along with Keith Johnstone and Viola Spolin, is considered one of the premier influences on Improvisational Theater. An actor, improviser, writer, and teacher, he was a co-author of the book Truth in Comedy along with partner Charna Halpern , which contained techniques that are now common to long-form improvisational theater and described the overall structure of "the Harold" which remains a common frame for longer improvisational scenes.

Close began improvising and directing with the Compass Players, and later directed at The Second City. Along with Charna Halpern, he co-founded the ImprovOlympic. Acolytes of Del Close have gained prominence in the field of comedy with astounding frequency. At any given time, roughly a quarter of SNL's cast is composed of former Del Close trainees.

Close had a prolific career, appearing in a number of films and television shows. With John Brent he recorded the classic beatnik satire album "How to Speak Hip," (Mercury, 1959) which became a prized record for DJs worldwide and was one of Brian Wilson's favourite comedy albums. He also co-authored the horror anthology Wasteland for DC Comics.

Close donated his skull in his will to the Goodman Theatre for use in Hamlet productions.