NEW YORK — Steve Martin has this funny theory about artists and careers, spelled out with comic timing.

“You kind of can always tell if someone hits a wall by their haircut,” he says.

Pause.

“And I’ll explain what I mean.”

Pause.

“Like if someone was doing really, really well in the ’70s, they keep their ’70s haircut. If they did well in the ’80s, if they keep their ’80s haircut. If they’re moving along, their haircut changes.”

Pause.

“Now, I’ve had the same haircut forever.”

And there goes the theory.

If Martin’s parted white hair — its evolution more a matter of age than of style — reflected his creative choices, it would have been an ongoing fashion show. Few contemporary writer-performers have succeeded in so many art forms: standup comedy, movie acting, television acting, playwriting, novel writing, with time made throughout for banjo playing.

His passions now include cartoon captions, honed through a collaboration with the New Yorker cartoonist Harry Bliss, brought together at the recommendation of mutual friend and New Yorker art editor Françoise Mouly.

“She calls me and says that she was having dinner with Steve Martin and he had some cartoon ideas and was I interested in drawing a couple of them up,” Bliss said. “We started emailing back and forth and he sent me a couple of ideas — one I remember was about a dog panhandling. And we both kind of laughed. There was that initial spark. It was fun.”

Martin and Bliss spoke recently during an afternoon interview in midtown Manhattan, across the street from the New York Public Library’s main branch. Friendly for the past few years — “five years ago” was Martin’s favorite response when asked for any kind of timeline — they have formed a professional kinship built upon Martin’s words, Bliss’ images and a shared love for the satire and well-populated illustrations of Mad magazine.

They first worked together on the bestselling “A Wealth of Pigeons,” published in 2020, and now have completed “Number One Is Walking.”

The title is the premise for the kind of Hollywood joke Martin has mastered. The words refer to a given actor’s status on set (at least some sets): “Number one is walking,” an assistant director might say to let others know of the lead actor’s whereabouts. Martin was “Number One” in “The Jerk,” “Bowfinger,” “Bringing Down the House” and others, only to be knocked back when he co-starred with Meryl Streep and Alec Baldwin in “It’s Complicated.”

“Number three is walking,” he heard.

Bliss says his greatest challenge for the book was to “put the fan away, and just listen to Steve tell the story.” The first half of “Number One Is Walking” is a meta-movie scrapbook, with Bliss’ sketches accompanying Martin’s memories of his film career and illustrating the making of the book.

A strip might begin with Bliss asking Martin about a specific project, such as “Roxanne,” or make light of which of the two is more famous.

“So, Harry, how did you get started cartooning?” Martin is seen asking on one panel, looking out dispassionately from a loveseat, with Bliss in a wicker chair at his side.

“Well, I …” says Bliss, rising eagerly from his seat.

“That reminds me,” Martin interrupts, “of when I did the movie ‘Dirty Rotten Scoundrels.”‘

Martin shares memories of such late friends as Carl Reiner, Charles Grodin and Robin Williams. He offers a vivid account of meeting Mike Nichols, the original director for “The Jerk” (Reiner ended up with the job) and later his director when Martin and Williams starred in a 1988 stage production of “Waiting for Godot.” Nichols, Martin explained during the interview, was always the wittiest man in any gathering, “the Mike Nichols in the room, the number one wit.”

“I was very nervous to meet Mike Nichols,” he recalled. “And we’re going to walk to dinner. And it’s summer. And it’s New York, so we’re outside and it’s warm and I have no idea what to say to him.”

“So I say, ‘Wow, this weather is great.’ And he said, ‘Yes, isn’t it ironic,'” Martin continued.

The book’s second half continues the kind of riffs Martin and Bliss created for “A Wealth of Pigeons.” A given cartoon might begin with Martin emailing a funny caption — sometimes in the middle of the night — and Bliss devising the image to go with it.

For Bliss, the blessing and occasional burden of Martin’s captions is that they originate from the mind of, well, Steve Martin: “Why Euclid had no friends,” or “Various entrances to the gates of hell,” or “The Evolved Bee.”

“There was a time when I actually thought, ‘Why can’t Steve do a simple (caption)?'” Bliss said.

“You didn’t like when I sent you an idea for 10,000 penguins coming down the Arctic slope,” Martin said, adding that even as he felt guilty for some of his ideas, he believed that suggesting the seeming impossible brought out “Harry at his best.”

“That’s when you kill,” Martin said.

The pair may well work together again, although neither is ready to announce future plans. Bliss very much has a day job at The New Yorker and is otherwise happy to remain a cartoonist, and only a cartoonist.

“I am not that ambitious,” he said. “I really have no desire to do much else.”

“I read a book in college called ‘The Psychoanalytics of Art,'” Martin observed. “It talked Picasso, who was constantly changing, constantly developing a new thing, and Chagall, who painted essentially the same things his whole life. It’s just a different style.”

“I don’t have this restless thing, (where I’m thinking) ‘I’ve got to keep changing,'” he added. “I don’t plan ahead. it just sort of happens.”