(CNN) In exploring the colorful comedy scene of the early 1970s, the new Showtime series "I'm Dying Up Here" presents a keen reminder of Johnny Carson's role -- unparalleled before or since -- in launching the careers of stand-up comics.

Carson moved "The Tonight Show" from New York to Los Angeles in 1972, and made a point of booking hot young comics. His approval was seen as the ultimate validation, and the difference between becoming a headliner and a one-way ticket back home.

Richard Belzer once called an "OK" sign from Carson at the end of a comic's set as "a gesture from God." The most coveted approbation, though, was being summoned over to the couch, an honor bestowed on only a handful of first-time performers.

In a New York Times piece after Carson's death in 2005, comic Jeff Cesario quipped that some comics studied Carson's reactions "like they were poring over the Zapruder film."

"My whole life changed," said Tom Dreesen, a veteran comic who toured with Frank Sinatra and is serving as a consultant on "I'm Dying Up Here," regarding the "euphoric feeling" of his first appearance. "There's no describing that first 'Tonight Show.' You knew that one appearance could not only make your career but break your career."

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