They both secured gigs writing jokes for Good Times star Jimmy Walker, and landed spots on the Tonight Show within a year of each other. Johnny Carson liked Letterman’s cool, underplayed act, and soon appointed Letterman as his guest host. Four years after he made his debut, Letterman landed his own show, Late Night. Leno, in contrast, played The Tonight Show four times in the late ’70s with diminishing returns. According to Bill Carter’s indispensible book The Late Shift, Leno’s manager, Helen Kushnick, made a tacit deal in the early ’80s with Letterman’s producers that gave Leno multiple annual guest spots on Late Night. He ended up appearing more than 40 times in a decade, exceeding any other guest on that show. As Carter notes, “David Letterman had helped launch his own career by watching Jay Leno work in clubs. Now Jay Leno was using his guest shots with Letterman to save his career.”

Leno’s appearances on Late Night, which have been extensively documented elsewhere, might come as a surprise for viewers who know him mainly as the middlebrow host of The Tonight Show. The persona that Leno honed in Letterman’s guest chair was loud, prickly, and so miffed at the inanities of modern culture that he could barely control himself. For his part, Letterman mostly set up Leno with leading questions and then sat back and let him riff. At the end of every segment, Letterman would ask what was bothering Leno that week, and Leno would rail against everything from lazy television tropes to the letters in Penthouse magazine. Leno’s appearances were so well known to Late Night viewers that Chris Elliott, then a writer and occasional performer on the show, once did a spot-on impersonation of a ranting Leno, foreshadowing the comedic punching bag that Leno would become.

A memorable guest spot from 1985 underscores the unique rapport that developed from their differing comedic sensibilities. Leno, in his snazziest Miami Vice attire (Seinfeld once stated that Leno “dresses like an Iranian disco owner”), launches into a diatribe on the idiocy of network television. Cutting him off, Letterman asks if there are any TV shows he actually enjoys. Leno replies, “Big fan of the news. In fact, a few nights ago I was watching that guy Schrader—” Before Leno can finish, Letterman says, “Big fan of the news? Is that what you said?” Deflecting Letterman’s question, Leno pivots to a polished bit on portable heart machines. Letterman chuckles halfheartedly, and then returns to his earlier line of inquiry:

Letterman: I didn’t realize you were a fan of the news. Leno: Yes, I am. Letterman: Do you write them letters and stuff? Leno: No, I don’t write them letters. Letterman: Do you have a favorite anchorman? Leno: Huh? No, I’m not psychotic! I don’t write—I have a notebook and I write, “All women are unclean” and mail this stuff. (Letterman laughs.) No, I watch the news for information! Letterman: But you said you were a big fan of the news. You made it sound like you were a little—Are you in a club? Leno: No, I don’t have a club. (Juts out his chin and sulks as the audience laughs.)

As he’s done many times, Letterman fixates on an innocuous, tossed-off phrase that becomes funny only through persistent repetition. It’s the sort of offbeat, punchline-free humor at which he excels. Leno at first tries to steer the conversation back to his routine, but Letterman’s doggedness forces Leno to ad-lib with him, albeit reluctantly. The arbitrary questions are a way for Letterman to pull Leno out of his joke-a-minute comfort zone.