David Letterman

David Letterman's opening monologue on 17 September 2001, the first Late Show after the attacks on New York, has no jokes. He speaks for several minutes about grief, courage and whether it was right to come back on air, then hands over to Dan Rather. It showed how an entertainer could help a frightened audience by dropping the act entirely, and many late-night hosts have since followed its example after tragedies.