Michael McDonald’s new memoir is titled “What a Fool Believes,” after the Grammy-winning hit he wrote in 1978 with Kenny Loggins.Credit...

Ariel Fisher for The New York Times

The voice of Michael McDonald has been compared to velvet, silk and sandpaper, melted chocolate and last year, by a besotted 11-year-old girl, an angel. He has harmonized with the best in the business. But his latest duet might cause even the most Botoxed foreheads of Hollywood to furrow.

“How you like us so far?” joked Paul Reiser, the actor and comedian, from one corner of a squishy sofa in McDonald’s Santa Barbara, Calif., aerie on a recent Tuesday morning. He was there to talk about the singer’s memoir, which they wrote together and will be published by Dey Street Books on May 21.

In the other corner, emanating the equanimity that’s as beloved as his baritone, was the man whose 50-plus-year career has included backup vocals for Steely Dan, Elton John, El DeBarge, Toto, Bonnie Raitt and on and on — backup so extensive and distinctive it’s inspired playlists on Apple Music and Spotify. He was wearing a paisley-patterned shirt, black trousers and, as one might expect of an angel who must tread this cursed Earth, puffy Hoka sneakers...

McDonald, 72, has also spent decades in the spotlight, albeit sidlingly, often with his famous blue eyes shut. (“Singing is such an intimate act,” he explains in the book, “and like kissing, it does no real good to see what the other person is doing.”) He led the Doobie Brothers in various iterations with his gospel-inflected keyboard style; released nine solo studio albums traversing multiple genres and continues to make live appearances at venues from Coachellato the Carlyle.

The book is titled “What a Fool Believes,” after the Grammy-winning hit McDonald wrote in 1978 with Kenny Loggins, though with some hesitation. “I thought, ‘Well, that’s just too obvious,’” he said. “I wanted it to be something clever and mind-provoking, and I couldn’t really think of anything because, you know, I have a problem provoking my own mind.”

He was convinced by Reiser, who among many other projects wrote the best-selling books “Couplehood” and “Babyhood” in the 1990s, and a follow-up, “Familyhood,” in 2011.

“I mean, how lucky am I?” McDonald said.

“Awwww,” Reiser said. But seriously: “He’s very introspective, which you don’t see at first and then you go, ‘Oh, this guy is deeper than you think.’” A beat. “Not that I thought you were shallow!”

As if in a marathon therapy session, they plunged together back to the past. McDonald grew up Irish Catholic, bracketed by two sisters in a suburb of St. Louis. His father was a streetcar driver and ex-Marine, a teetotaler with an eye for the ladies and a beautiful singing voice. His mother worked in a trading stamps store and had a weakness for pep pills. The marriage didn’t last.

He had an Aunt Mame with a Victrola from which, at age 5, he learned to imitate Mario Lanza warbling “Love is a Many-Splendored Thing”; an Aunt Bitsy who introduced him to Rodgers and Hammerstein; and an Aunt Ann Catherine whose record collection included, revelatorily, Ray Charles. Burt Bacharach was a big influence, too. Beatles-wise, he gravitated more toward McCartney than Lennon.

“I always related to him,” McDonald said, “because I could sense from him that he heard a lot of the same music I heard — that kind of barroom, Tin Pan Alley chord progression.”

In one devastating passage, McDonald writes of getting his girlfriend pregnant in eighth grade and biking over to confront her parents, who insisted, along with his own, that she give the baby up for adoption. Too young to sort through this emotional wreckage, he steered away. “Disappearing became my MO,” he writes. “Distancing myself from whatever it was that might require accountability.”

He dropped out of high school and joined a series of colorful-sounding bands — the Majestics, the Sheratons, the Delrays, the Guild, the Blue. Old ballrooms; natty threads. Beer and marijuana became staples, and later, after he moved to Los Angeles and began breaking into the big time, cocaine.

Referred to Steely Dan by the drummer Jeff Porcaro in 1973, he “came to rehearsal a few days later and knocked everyone out,” Donald Fagen, the band’s surviving founder, wrote in an email. “There was a serious discussion about whether he should replace me as the lead singer, which would have been my personal preference. But, for some dumb reason, I was voted down. I didn’t insist, and I’ve regretted it ever since. I mean, here’s this monster singer and musician, and he’s also really funny and a sweetheart of a guy. What’s not to like?”

Patti LaBelle called about recording “On My Own” (1986) with McDonald, after a solo version went sour. “I said, ‘The person I would love to sing it with is quiet, beautiful Michael,’” she remembered. Recently they crooned it together on a jazz cruise on the Norwegian Pearl where, she said, he confessed nerves beforehand; when he emerged onstage, the crowd went bananas. “He’s one of a kind. He comes out whispering and then — all this power. It’s like he doesn’t even open his mouth, he’s just so laid back.”

Indeed, so constitutionally low-key is McDonald that Loggins, with whom he also composed “This is It” and “I Gotta Try,” and who released his own memoir, “Still Alright,” in 2022, didn’t even know his old collaborator is about to join him on the bookshelves.

On the phone, Loggins remembered the first time he heard McDonald in the Doobies’ “Livin’ on the Fault Line.” “I just felt like, ‘Oh, this is going to be a major American voice,’” he said. “He kind of goes into a trance when we write, and if I say ‘play it again,’ he won’t remember, so I have to record all the time. We have completely different styles vocally, but blend really well. It’s not logical.”

In 2005, the duo, along with Hall and Oates, Christopher Cross, Toto, Steve Perry and others, were affectionately spoofed in J.D. Ryznar’s web series, “Yacht Rock.” A strain of the much-maligned catchall “adult contemporary” category was suddenly rebranded as “smooth music”: gleaming with high production values and a general mellifluence; the polar opposite of punk. McDonald was portrayed as the genre’s earnest common denominator: its anchor, its intergenerational secret sauce, who stumbles out of fashion and then rises again when “I Keep Forgettin’” is sampled by Warren Gin 1994.

McDonald compared the yacht-rock phenomenon to oldies radio. “Even though I was a little ambivalent about both, at first, they turned out to be the two best things that ever happened to us from the ’70s,” he said, “because we kept getting airplay.”

This wasn’t his first time as a figure of comedy. In 1981, in an SCTV sketch, Rick Moranis portrayed McDonald driving intently down a highway in a convertible to clap on headphones and sing bits of backup for Cross’s “Ride Like the Wind” before rushing off to his next gig. McDonald contributed a song to the 1999 “South Park” movie and sang at a fictional “30 Rock” benefit. In “The 40-Year-Old Virgin” (2005), an electronics-store manager played by Jane Lynch is excoriated by an employee for broadcasting a McDonald concert video ad nauseam. (“If I have to hear ‘Yah Mo B There’ one more time I’m going to yah mo burn this place to the ground!”) And in 2013 Jimmy Fallon and Justin Timberlake donned silver McDonald wigs to sing “Row, Row, Row Your Boat” with him.

We have his current writing partner to thank, or blame, for the chapter title “Doobie or Not Doobie, That Is the Question.” Reiser, an accomplished musician himself who can sit down at the Yamaha and spontaneously ripple off a Rachmaninoff concerto, first encountered McDonald performing during an event at a neighbor’s house. “And in a surge of moxie, I went, ‘I live literally next door, and I got a music studio with two pianos that I put in just in case this ever happened,’” Reiser recalled. “Would you like to come over?’”

A jam session ensued. A friendship developed. Then the pandemic descended. McDonald thought that during lockdown he might apply himself with renewed vigor to his painting hobby. Reiser had another idea. “He’s the only reason the book exists, as far as I know,” McDonald said. “Putting one foot in front of the other was never my strong suit, on my own power. By myself, I become like a blob.”

McDonald’s wife, the singer Amy Holland, wandered briefly into their living room, which is large, cozy and barnlike, with plenty of blankets and candles and a banjo mounted on the wall bearing the visage of her mother, Verna Sherrill Boersma, who did a hillbilly routine as Esmereldy in the 1940s and resembled …. was it Bette Davis? “Celeste Holm,” McDonald said.

He and Holland were married in 1983, with the lead singer of Ambrosia performing “Biggest Part of Me” at the reception. They have two adult children, a submissive golden retriever, and a possessive Chihuahua who sleeps in between the couple.

One of their previous pooches cringed at his singing, McDonald noted, and would try to pry his master’s hands off the piano keys every time he played.

“Everyone’s a critic,” Reiser said.

Working with McDonald, he said, was often just a process of having him slow down and fill out anecdotes that, to him, seemed like no big deal — Steely Dan partying in the penthouse of a London hotel, for one. “I’m going, ‘That’s like a Fellini movie!’” One chapter is devoted to an extended bender with the band’s co-founder, Walter Becker, who died in 2017; another features an unintentional acid trip. (David Gest also makes an appearance.)

“I remember looking to the guys who seem to manage it well — guys who did a little of this and did a little of that but didn’t have a problem like I suspect that I already did,” McDonald said. “Their whole thing was ‘You just got to manage it — you can’t overdo it, man.’” He paused. “And every one of those guys, to a man, is gone.”

Sober since the mid-80s — he said his current vices are “food and sloth” — McDonald is not only still here, but discreetly ubiquitous.

Forget about velvet and silk: The more you read and think and listen, the more his voice seems like a connecting thread running through America’s popular-music tapestry that, if pulled, might unravel the whole thing — or at least, leave a significant, unmendable hole.

And yet, he said, “to this day I keep expecting the doors to fly open and the impostor police to come and grab me and take me out.”

Alexandra Jacobs is a Times book critic and occasional features writer. She joined The Times in 2010. More about Alexandra Jacobs