On Johnny Carson’s Tonight Show, talent coordinator Jim McCawley’s job was to root through comedy clubs for fresh standup meat. On a November in ‘78, he suggested I stick around to catch the intense young man awaiting the cue to uncork his initial six-minute chunk before his idol.

“Will you welcome…Mr. David Letterman.”

Letterman’s set killed, and Johnny invited him soon after to guest host. Meanwhile NBC was prowling for someone to keep viewers sleepless for another hour. In ‘82 Dave got the call.

Late Night rejiggered the format. The playbook: a tightly controlled, ostensibly out-of-control, random chaos. Johnny tucked America in. Letterman’s comedy was caffeinated. Loathing showbiz values of ersatz sincerity, he helmed an unsentimental program. The premise: Everyone’s out to screw us, so let’s get ours first. He mocked the institution’s cherished codes, tossing top-ten cards through the back window accompanied by a sound effect of broken glass. He wandered out from behind the desk into New York’s streets in a wise guy strut waving a cigar…a prop that implied, “I’m in your face and don’t give a damn”.

A student of the genre, he incorporated bits from The Tonight Show’s first host, Steve Allen. Steve had given audience members salamis. He handed out hams. Steve had jumped into a vat of Jell-O. He stuck himself to a Velcro wall. He built on Carson’s popular animal segments with a seemingly hapless zookeeper, Jack Hanna.

The music had a different look. The Tonight Show reflected Carson’s taste in mainstream singers and jazz performers. Late Night had a soft spot for country, roots rock, and R & B artists. Veteran actors and Vegas comics seldom got invited to the party.

Dave’s irony attracted a hard-core niche of college kids. Late Night became the hip hang and guests unwilling to walk into the Letterman propeller need not apply. He was a publicist’s nightmare when he jettisoned pre-interview notes and penetrated a jittery star’s carefully cultivated veneer. The vacuous didn’t get their humiliating takedown until they watched the playback later in their hotel rooms.

In ‘95 I invited Johnny to lunch for his 70th birthday at a restaurant in Malibu. Letterman, having lost The Tonight Show to Jay Leno, had begun The Late Show at CBS. Johnny had hoped he’d inherit his job, but NBC chose Jay. The helicopter dad in him was critiquing his protégé.

David’s on self-destruct and it may be too late to pull out. He’s consistently two ratings points behind Leno. People won’t want to say they watch him among their friends and he’ll never get them back. He’s changed since he went over to CBS. He makes his staff stay after the show each night to analyze it. And the way he makes fun of people. I could never do that.

Johnny was a lot more sarcastic than his on-air persona, but he couldn’t bring himself to ridicule his fans.

“I didn’t like how he handled hosting the Oscars. You’re at their event. You have to respect it”.

Then on the Letterman reclusiveness. “I’m private, but David is secret”.

Former friends Dave and Jay were mano-a-mano at 11:30. Jay plowed a safer middle ground, his monologue stuffed with applause lines few could disagree with, and he gained a broader viewership. A team player, he gladly showed up at affiliate gatherings. Dave was churlish.

Over the years Letterman’s monologues tilted left of center. Johnny was a political southpaw too but never let it show. It may have been Dave’s strategy to peel off a piece of Jon Stewart’s audience. More likely in the winter of his career he didn’t much care what people thought of him. George Bush has been out of office over six years and the most worn-out key on his writers’ keyboards is still the W. In his final weeks he loaded the guest list with Michelle and Barack Obama and Bill Clinton. (Joseph Stalin sent regrets that he would have loved to appear but he was dead.)

Last year, NBC gave Leno his Jay-walking papers, replacing him with a new gunslinger, Jimmy Fallon, a performer more in the mold of a Carson. The Tonight Show was moved back to 30 Rock. Dave, once New York’s darling, now had to compete for younger guests. At ABC in LA, the other Jimmy, Kimmel, who idolized Letterman, had become another rival.

Like music, each generation has its own comedy and now its own delivery system. Where Carson jokes had been retold the next morning at water coolers, Fallon and Kimmel clips are posted on YouTube. Dave resisted marketing himself on social media despite the ratings challenge. Fallon averages nearly four million nightly viewers, Letterman and Kimmel about 2.7 million each.

Hosting a talk show is harder than it looks. When guests forget that hilarious anecdote they were expected to tell, you’re only a second from dead air. The best advice one can give a new host or guest host is listen to what the guest is saying and not look down to read the next question. Don’t ask me about Liberace.

After Dave gave himself the hook, he seemed at peace with the decision, even sharing tales of fishing with his son Harry. He became comfortable in his own skin, or maybe as comfortable as he’ll ever get. 33 years is a remarkable run. The Chevy Chase Show was cancelled after five weeks. David Letterman’s iconoclastic spirit inhabits the many comics he’s influenced, and his reign added an amendment to the Talk Show Constitution. That’s not a bad legacy.

Raymond Siller was the longtime head writer on The Tonight Show Starring Johnny Carson.