Bonnie Franklin, left, MacKenzie Phillips,second from left, Valerie Bertinelli and Pat Harrington Jr., right, of the 1970's television sitcom "One Day at a Time, " were reunited for a segment of the NBC "Today" television program in 2008. (RICHARD DREW/ASSOCIATED PRESS)

Pat Harrington Jr., an actor and comedian who portrayed the farcically macho building superintendent Dwayne Schneider in “One Day at a Time,” a sitcom that explored sexism, harassment and other tribulations through the lens of a divorced working woman and her two teenage daughters, died Jan. 6 in Los Angeles. He was 86.

His daughter Tresa Harrington announced the death on her Facebook page but did not provide other details. In November, she wrote that he had Alzheimer’s disease and was in rapidly declining health.

Although billed as a supporting actor on “One Day at a Time,” Mr. Harrington provided such welcome comic relief that the program’s popularity and longevity — it aired on CBS from 1975 to 1984 — was owed as much to him as to anyone. Years afterward, producer Norman Lear, who also created “All in the Family,” said Mr. Harrington “turned out to be the comic strength of the show.”

Seemingly coming from nowhere — he was a total unknown to Lear when the show was being cast — Mr. Harrington was in fact a seasoned comic performer. His father had been a song-and-dance man in vaudeville and on Broadway, a late-night carousing companion of fellow Irish American entertainers such as Bing Crosby, Pat O’Brien and James Dunn.

“They’d sit down for eggs as I’d be going off to parochial school,” Mr. Harrington once recalled.

”One Day at a Time,” which ran on CBS from 1975-1984, followed Ann Romano (Bonnie Franklin, lower right) who moved with her two teenage daughters, Julie (Valerie Bertinelli, center) and Barbara Cooper (MacKenzie Phillips, upper right) back to her hometown of Indianapolis to start fresh after her divorce. Dwayne Schneider (Pat Harrington Jr., left) is the super of the building who becomes close friends with the women. (HO/CBS)

In the late 1950s, his talent for wisecracking and mimicry brought him influential admirers such as Jonathan Winters, Jack Paar, Steve Allen and Danny Thomas. He subsequently worked in nightclubs, released comedy albums, and won small roles in films such as “Easy Come, Easy Go” (1967) with Elvis Presley and “The Candidate” (1972) with Robert Redford.

But it was “One Day at a Time” that made Mr. Harrington a household name during its protracted prime-time run.

The star was Bonnie Franklin, playing an independent-minded divorced woman in Indianapolis who struggles to raise two willful daughters (played by Mackenzie Phillips and Valerie Bertinelli). Set against the second wave of feminism, the show explored previously taboo sitcom subjects such as divorce, rape, teenage pregnancy and menopause.

Franklin’s Ann Romano is both sensible and exasperated as she juggles a career, her home life and come-ons from men such as Mr. Harrington’s Schneider, a seedy building custodian who tells her, “The ladies in this building don’t call me ‘super’ for nothing.”

Rendered by Mr. Harrington, Schneider was less a threatening wolf than a clueless chauvinist. Fancying himself a ladies’ man, he sports a Clark Gable-inspired pencil mustache and swaggers about with his tool belt around his waist and a cigarette pack tucked in the sleeve of his white T-shirt.

As the character was conceived, Schneider was a married man and an unrepentant adulterer who used fake maintenance problems to enter women’s apartments. Mr. Harrington, however, doubted that such an unpleasant type would fit in a show filled with far more likeable people.

On Mr. Harrington’s insistence, Schneider was recast as a bachelor with a comically grandiose sense of his appeal to the opposite sex. “At first, Schneider was pretty much a lecher,” he told People magazine. “I made sure that got changed to ‘amorous.’ It bespeaks a certain respect for women.”

Over the years, Schneider surrenders his pursuit of Romano and becomes a surrogate father figure to her daughters. In the show’s final year, Mr. Harrington won an Emmy Award for outstanding supporting actor in a comedy series.

Daniel Patrick Harrington Jr. was born in Manhattan on Aug. 13, 1929. He grew up watching his father’s career wax and wane.

“Until I was schoolage, we drove around the country in a Hupmobile and Dad worked week to week, hand to mouth by singing, playing drums and entertaining,” he told Robert Pegg, author of the book “Comical Co-Stars of Television.” “He didn’t want that for his kids because he knew it was a very hard life.”

Mr. Harrington went to a Catholic military school and graduated from Fordham University, where he also later received a master’s degree in political philosophy. After Air Force service, he began working in the NBC mail room, a job he parlayed into a junior advertising salesman position for the network.

He told Pegg that he drew notice for his elaborate office pranks. He once paid an actor $20 to impersonate David Sarnoff — who was chairman of the parent company of NBC and was universally known as “the General” — to approach him one morning before a weekly sales-staff meeting.

“How are sales?” the imposter Sarnoff asked.

In a move that might have been career suicide, Mr. Harrington shot back with annoyance, “Why don’t you just get back upstairs and tend to your electrons and I’ll take care of sales.”

“Good for you, young man,” Sarnoff replied, patting his shoulder. “That’s the spirit!”

Mr. Harrington then strutted past aghast colleagues, quipping, “Look, I’ll be out for the rest of the day.”

He often entertained clients at Toots Shor’s, the Manhattan watering hole, where, as the evenings wore on, he liked to trot out various voices and characters. He had his greatest success conjuring a fictional Italian immigrant named Guido Panzini, part of a gag he honed over many years and many drinks.

Panzini was at times the self-preserving first mate of the doomed ocean liner Andrea Doria, a charming golf pro who once played the toughest course in the world — up the side of Mount Kilimanjaro — and a veteran of the Italian submarine service in World War II who learned English by sneaking up on American warships at night to watch movies.

Winters, who was scheduled to substitute host on Paar’s variety show, caught the routine one night and booked him in 1958. That appearance sparked widespread demand for Panzini to appear on other shows.

Mr. Harrington so completely inhabited the Panzini character — and his style was so deadpan — that an official with the U.S. immigration service reportedly expressed concern to the network that the agency could find no record of his entry into the country.

Over the next few years, Mr. Harrington became part of the ensemble on “The Steve Allen Show” and won a recurring role as Thomas’s son-in-law on the sitcom “The Danny Thomas Show.”

In addition to many theater parts, he did voice-over work for cartoons, made a spate of game-show appearances and had a frequent role in the early 1970s as a prosecutor on “Owen Marshall, Counselor at Law,” an ABC legal drama starring Arthur Hill.

His first marriage, to Marjorie Gortner, with whom he had four children, ended in divorce. In 2001, he wed Sally Cleaver, an insurance executive. A complete list of survivors was not immediately available.

In recent years, Mr. Harrington popped up as a guest on TV shows such as “Curb Your Enthusiasm” and “Hot in Cleveland.” But in a varied career, he made his peace with being associated with a single sitcom, “One Day at a Time,” emphasizing that it had brought him steady work in a notoriously unsteady profession.

He told Pegg, “I got 10 years of work out of this series, and if I was penalized by typecasting, then that’s the price you have to pay.”