NBC's venerable late-night talk show The Tonight Show has provided a unique window into the changing times and mores of contemporary American culture. Beginning in 1954, its four principal hosts have used the program as a pulpit for nightly commentary on events both profound and piddling. Over the decades, the show has fluctuated wildly in terms of its influence and quality. At various times it offered groundbreaking comedy, scintillating conversation, and instructions for stylish living. Even Jay Leno's tepid, non-threatening Tonight Show of the 1990s seemed somehow to reflect the tenor of its self-satisfied times.

The first host of The Tonight Show was Steve Allen, a former disc jockey who had presided over a succession of Golden Age TV offerings. During his innovative three-year run as host, Allen established the program's basic format: a monologue followed by a comedy set piece and a series of...