Del P. Close (March 9, 1934 – March 4, 1999) was an American actor, writer, and teacher who coached many of the best-known comedians and comic actors of the late twentieth century. In addition to a prolific acting career in television and film, he was considered a premier influence on modern improvisational theater. Close co-authored the book Truth in Comedy, which outlines techniques now common in longform improvisation, and describes the overall structure of "Harold", which remains a common frame for longer improvisational scenes.