Michael Constantine, an Emmy-winning character actor who played a wry high school principal on the TV series “Room 222” and starred three decades later as the Windex-obsessed, endearingly overbearing dad in “My Big Fat Greek Wedding,” died Aug. 31 at his home in Reading, Pa. He was 94.

His agent, Julia Buchwald, confirmed the death but did not give a cause.

A beetle-browed veteran of stage and screen, Mr. Constantine appeared in a half-dozen Broadway plays and more than 180 movies and television shows. He started out playing murderers, mobsters and other heavies — including the pool-hall character Big John in “The Hustler” (1961), with Paul Newman — before taking good-guy roles as solemn lawmen and comically dyspeptic authority figures.

At age 42, he landed his breakout role in the ABC comedy-drama “Room 222,” which premiered in 1969 and ran for five seasons. Created by James L. Brooks, the series starred Lloyd Haynes as a history teacher who preaches tolerance and understanding to his students, in what was then a rare leading role for an African American on prime-time TV.

The show also featured Denise Nicholas as a high school guidance counselor and Karen Valentine as a student teacher, with Mr. Constantine as the cynical but charming Principal Seymour Kaufman. He won an Emmy Award for best supporting actor in a comedy in 1970 and was nominated again for the show’s second season.

Nearly two decades later, he told the Los Angeles Times that he was sometimes approached by schoolteachers who thought he was a real-life principal. “They say, ‘I worked for you, but I can’t remember at which school.’ ”

Mr. Constantine became best known for playing Gus Portokalos, the traditionalist patriarch who insists that his oldest daughter, Toula (Nia Vardalos), marry a nice Greek man in “My Big Fat Greek Wedding” (2002). “There are two kinds of people,” he reminds her: “Greeks, and everybody else who wish they was Greek.”

Adapted from a one-woman play by Vardalos, who wrote the screenplay, “My Big Fat Greek Wedding” was shot for $5 million and became a sleeper hit, making nearly $370 million worldwide. It remains the highest-grossing romantic comedy in history and one of the most successful independent movies ever made. “There is so much goodwill here, you are charmed as much as tickled into laughing,” Desson Howe wrote in a review for The Washington Post.

Mr. Constantine credited the movie’s success in part to its depiction of “unconditional familial love.” A son of working-class Greek immigrants, he said he drew on memories of his mother in developing his character, a disciplinarian who exalts Greek culture and insists that any word can be traced back to a Greek root — even the Japanese word kimono.

Although he is initially shocked by Toula’s choice of husband, a WASP schoolteacher named Ian Miller (John Corbett), he eventually comes around to the groom, delivering a wedding toast in which he says that the name Miller derives from the Greek word for apple, while Portokalos comes from the Greek word for orange. “We’re all different,” he concludes, “but in the end, we’re all fruit.”

Improbably, his character was also convinced that Windex could treat not just dirty windows but any physical ailment, “from psoriasis to poison ivy,” as Toula puts it. In the wake of the movie’s success, Mr. Constantine told United Press International, “I can’t walk into a room without people asking me, ‘Did you bring the Windex?’ ”

By many accounts, he was born Constantine Joanides (his last name is sometimes Romanized as Ioannides) in Reading on May 22, 1927. Some sources give his birth name as Gus Efstration. Mr. Constantine said he first acted under the name Michael Barr, drawing from the last name of his idol, actor John Barrymore, before settling on Michael Constantine and changing it legally.

His father was a steelworker, his mother a homemaker, and the family only spoke Greek at home. “I was so discouraged as a boy, I remember thinking how out of place I seemed,” he told the Boston Globe in 1972. “No wonder. I couldn’t speak English until I was 7.” He revealed his new language skills by blurting out a profanity, leading his mother to punish him by putting pepper on his tongue.

After graduating from high school, Mr. Constantine moved to New York to try his hand in acting. He made his Broadway debut in 1955, rising from extra to understudy for star Paul Muni in “Inherit the Wind.” Over the next decade he appeared in four more Broadway plays, including as three separate characters in “Compulsion,” based on the Leopold and Loeb murder case, and as the director of a school for the blind in “The Miracle Worker.”

As he launched his acting career, Mr. Constantine supported himself by working as a night watchman at a department store, counterman at a hamburger chain and barker at a shooting gallery. He made his film debut in the prison melodrama “The Last Mile” (1959), starring Mickey Rooney, and soon moved to Hollywood.

He went on to appear in movies including “Don’t Drink the Water” (1969), “Voyage of the Damned” (1976), “My Life” (1993) and “The Juror” (1996), playing a judge in a mafia trial opposite Demi Moore and Alec Baldwin. That same year, he appeared in the Stephen King adaptation “Thinner,” as a white-haired 106-year-old who places a curse on a lawyer (Robert John Burke).

On television, he appeared in shows including “The Untouchables,” “The Twilight Zone,” “Perry Mason” and “Law & Order.” He also had a recurring role as a tetchy photographer on the 1960s NBC sitcom “Hey, Landlord” and starred as a judge in “Sirota’s Court,” a short-lived precursor to “Night Court.”

Mr. Constantine had two children from his first marriage, to actress Julianna McCarthy, a castmate in “Inherit the Wind.” That marriage ended in divorce, as did his second, to Kathleen Christopher. Information on survivors was not immediately available.

With the success of “My Big Fat Greek Wedding,” he and many of his castmates reprised their roles in a CBS sitcom, “My Big Fat Greek Life” (2003), and in a movie sequel, “My Big Fat Greek Wedding 2” (2016), in which his character boasted that “the Greeks invented hockey.”

Mr. Constantine embraced Greek culture in real life as well, although he was perhaps a less fiery partisan. While visiting his hometown in the 1980s, long before he played Gus Portokalos, he was invited to a Greek wedding in his old neighborhood. “Wild horses couldn’t have kept me away,” he later told the San Diego Union-Tribune. “I danced. I sang. I had a ball. It was sublimely, soul-nourishingly Greek.”