Michael Constantine, an Emmy-winning character actor known as the genially dyspeptic school principal on the popular TV series “Room 222” and, 30 years later, as the genially dyspeptic patriarch in the hit film “My Big Fat Greek Wedding,” died on Aug. 31 at his home in Reading, Mass. He was 94.

His death was from natural causes, his agent,Julia Buchwald, said.

Mr. Constantine, who began his career on the Broadway stage, was endowed with fierce eyebrows, a personal warmth that belied his perennial hangdog look, and the command of a babel of foreign accents. Of Greek American extraction, he was routinely cast by Hollywood to portray a welter of ethnicities.

Over time, Mr. Constantine played several Jewish characters, winning an Emmy in 1970 for the role of Seymour Kaufman, who presided with grumpy humanity over Walt Whitman High School on “Room 222,” broadcast on ABC from 1969 to 1974.

He also played Italians, on shows including “The Untouchables” and “Kojak”; Russians, as on the 1980s series “Airwolf”; a Gypsy in the 1996 horror film “Thinner,” adapted from Stephen King’s novel; and, on occasion, even a Greek or two.

Mr. Constantine, possessed of a gravitas that often led to him being cast as lawyers or heavies, starred as the night-court judge Matthew Sirota on “Sirota’s Court,” a short-lived sitcom shown on NBC in the 1976-77 season.

He had guest roles on scores of other shows, including “Naked City,” “Perry Mason,” “Ironside,” “Gunsmoke” and “Hey, Landlord” in the 1960s, and “Remington Steele,” “Murder, She Wrote” and “Law & Order” in the ’80s and ’90s.

On film, he appeared in “The Last Mile” (1959), a prison picture starring Mickey Rooney; “The Hustler” (1961), starring Paul Newman; “If It’s Tuesday, This Must Be Belgium” (1969); “Don’t Drink the Water” (1969); and “Voyage of the Damned” (1976).

Mr. Constantine became known to an even wider, younger audience as Gus Portokalos, the combustible, tradition-bound father whose daughter is engaged to a patrician white Anglo-Saxon Protestant in the 2002 comedy “My Big Fat Greek Wedding.”

An immigrant who made good as the owner of a Chicago diner, Gus is an ardent amateur etymologist who can trace any word to its putative Greek origin. (“Kimono,” he concludes after pondering the matter, surely comes from “cheimónas” — Greek for winter, since, he explains in his heavily accented English: “What do you wear in the wintertime to stay warm? A robe!”)

Gus is also a fervent believer in the restorative power of Windex, applied directly to the skin, to heal a panoply of ailments like rashes and boils.

“He’s a man from a certain kind of background,” Mr. Constantine said of his character in a 2003 interview with The Indianapolis Star. “His saving grace is that he truly does love his daughter and want the best for her. He may not go about it in a very tactful way. So many people tell me, ‘My dad was just like that.’ And I thought, ‘And you don’t hate him?’”

“My Big Fat Greek Wedding,” which also starred Lainie Kazan as Gus’s wife and Nia Vardalos and John Corbett as the young couple, was a surprise international hit. The film took in more than $360 million worldwide, becoming one of the highest-grossing romantic comedies of all time.

Mr. Constantine reprised the role on television in “My Big Fat Greek Life,” a sitcom that appeared briefly on CBS in 2003, and on the big screen in “My Big Fat Greek Wedding 2” in 2016.

The son of Theoharis Ioannides, a steelworker, and Andromache Foteadou, Mr. Constantine was born Constantine Ioannides in Reading, Pa., on May 22, 1927. (The family name is sometimes Romanized Joanides.)

He settled early on an acting career, an idea reinforced after a youthful visit to a friend who was studying acting in New York.

“I just knew I belonged there,” Mr. Constantine told Odyssey, an English-language magazine about Greek life, in 2011. “They could make fun of this hick from Pennsylvania, but I just belong here — this is me.”

The young Mr. Constantine studied acting with Howard da Silva, supporting himself with odd jobs, among them night watchman and shooting-gallery barker. He became an understudy to Paul Muni playing the character modeled on the famed defense lawyer Clarence Darrow in “Inherit the Wind,” which opened on Broadway in 1955.

In “Compulsion” — a 1957 Broadway dramatization of Meyer Levin’s novel about the Leopold and Loeb murder case — Mr. Constantine took over the role of the defense lawyer from Frank Conroy just before opening night. (Mr. Conroy withdrew after suffering a heart attack during previews.)

“Michael Constantine gives an excellent performance as the prototype of Clarence Darrow,” Brooks Atkinson wrote in The New York Times. “He avoids the sentimentality that the situations might easily evoke and plays with taste, deliberation, color and intelligence.”

Mr. Constantine’s other Broadway credits include Anagnos, the director of the Perkins Institute for the Blind in the original cast of “The Miracle Worker” (1959), and Dogsborough in Bertolt Brecht’s antifascist satire “Arturo Ui” (1963).

Mr. Constantine’s first marriage, to the actress Julianna McCarthy, ended in divorce, as did his second, to Kathleen Christopher. His survivors include two sisters: Patricia Gordon and Chris Dobbs, his agent said. A complete list of survivors was not immediately available.

For all Mr. Constantine’s credits, for all his critical acclaim, it was for a single role — and for a single prop wielded in the course of that role — that he seems destined to be remembered.

“I can’t tell you,” he said in a 2014 interview with his hometown paper, The Reading Eagle, “how many times I’ve autographed a Windex bottle.”

Alyssa Lukpat contributed reporting.