His death was confirmed by his stepson Randy Wilson.
At one time a heavy smoker, Mr. Klugman had survived throat cancer, which was diagnosed in 1974. After a vocal cord was removed in 1989, his voice was reduced to a gravelly whisper.
Mr. Klugman, who grew up in a rough-and-tumble neighborhood in Philadelphia, wasn’t a subtle performer. His features were large and mobile; his voice was a deep, earnest, rough-hewed bleat. He was a no-baloney actor who conveyed straightforward, simply defined emotion, whether it was anger, heartbreak, lust or sympathy.
That forthrightness, in both comedy and drama, was the source of his power and his popularity. Never remote, never haughty, he was a regular guy, an audience-pleaser who proved well-suited for series television.
Mr. Klugman was already a decorated actor in 1970 when he began co-starring in “The Odd Couple,” a sitcom adaptation of Neil Simon’s hit play about two divorced men — friends with antagonistic temperaments — sharing a New York apartment. (A film version was released in 1968 with Walter Matthau reprising his Broadway performance as Oscar.)
Opposite Mr. Klugman’s Oscar, an outgoing slob with a fondness for poker, cigars and sexy women, was Tony Randall as the pretentious fussbudget Felix Unger (spelled Ungar in the play and the film).
He also had more than 100 television credits behind him, including four episodes of “The Twilight Zone” and a 1964 episode of the legal drama “The Defenders,” in which he delivered an Emmy Award-winning performance as a blacklisted actor.
In the movies he had been the nouveau-riche father of a Jewish American princess (Ali MacGraw) in “Goodbye, Columbus” (1969); a police colleague of Frank Sinatra’s in “The Detective” (1968); Jack Lemmon’s Alcoholics Anonymous sponsor in “Days of Wine and Roses” (1962); and a murder-trial juror, alongside Henry Fonda, in “12 Angry Men” (1957).
In his solo moment in that film, his character, known only as Juror No. 5, recalls growing up in a tough neighborhood and instructs his fellow jurors in the proper use of a switchblade, a key element in their deliberations.
The “Odd Couple” series made Mr. Klugman a celebrity, but not immediately. During its five-year run, it never cracked the Top 20 in the Nielsen prime time ratings. Some critics said Mr. Klugman and Mr. Randall were always operating in the long shadows of the actors who came before them in the roles: besides Mr. Matthau as Oscar, Mr. Lemmon (film) and Art Carney (Broadway) had played Felix. But after “The Odd Couple” went into seemingly perpetual reruns, it earned a huge new following.
Mr. Klugman won two Emmys for the show and Mr. Randall one, and they eventually became the Oscar and Felix most identified with the roles.
“Quincy, M.E.” was as sincere a drama as the “The Odd Couple” was a loopy comedy, and though it is not remembered as fondly, its initial run, from 1976 to 1983, was far more successful. The title character, the medical examiner for Los Angeles County (Quincy’s first name was never revealed), was inspired by the real medical examiner at the time, Thomas T. Noguchi, known familiarly as “the coroner to the stars,” who performed autopsies on Marilyn Monroe, Robert F. Kennedy, Natalie Wood and John Belushi, among others.      
Mr. Klugman’s path to success was serendipitous. He was born in Philadelphia on April 27, 1922, the youngest of six children of immigrants from Russia. Most sources indicate that his name at birth was Jacob, though Mr. Klugman said in an interview that the name on his birth certificate is Jack.
His father, Max, was a house painter who died when Jack was 12. His mother, Rose, was a milliner who worked out of the family home on the city’s hardscrabble South Side, where Jack grew up shooting pool, rolling dice and playing the horses. His interest in acting was kindled at 14 or 15 when his sister took him to a play, “One Third of a Nation,” a “living newspaper” production of the Federal Theater Project about life in an American slum; the play made the case for government housing projects.  He appeared on four episodes of The Twilight Zone in the late 1950s and early 1960s which were widely popular with audiences.
In 1953, Mr. Klugman married the actress Brett Somers. They separated in 1974 (she played Oscar Madison’s former wife on “The Odd Couple”) but were never divorced. She died in 2007. Their two sons, Adam and David, survive him. In 2008 Mr. Klugman married his longtime partner, Peggy Crosby. She survives him as well, as do two stepsons, Mr. Wilson and Phil Crosby Jr., and two grandchildren.
Mr. Klugman returned to the theater in the 1980s, touring in a one-man show based on the life of Lyndon B. Johnson and replacing Judd Hirsch on Broadway as a crusty, bench-sitting old man in Herb Gardner’s play “I’m Not Rappaport.” He also starred in the television series “You Again?,” in which he played a long-divorced man whose 17-year-old son (John Stamos) moves in with him. The show lasted two seasons.
After his vocal cord surgery, Mr. Klugman was prepared to devote himself to raising racehorses, a longtime side pursuit; one of his horses, Jaklin Klugman, finished third in the 1980 Kentucky Derby. But with therapy he regained his voice and returned to the stage, appearing with Mr. Randall in a benefit performance of “The Odd Couple” in 1991.
He and Mr. Randall also reunited for a 1997 revival of “The Sunshine Boys,” Neil Simon’s comedy about a couple of crotchety old vaudevillians, produced on Broadway by Mr. Randall’s repertory company, the National Actors Theater. In 2005, the year after Mr. Randall died, Mr. Klugman published “Tony and Me,” a memoir.
Mr. Klugman, who always said he preferred acting in the theater, recalled initially turning down the television role in “The Odd Couple.” He wanted to do a play instead. But when the play quickly closed, he reconsidered; he needed the money.
Even so, Mr. Klugman wasn’t known as a comic actor, and by then Mr. Randall wanted Mickey Rooney for the role of Oscar. It took the producer, Garry Marshall, to persuade Mr. Randall that Mr. Klugman was right the part. He had seen Mr. Klugman do comedy, Mr. Marshall said, referring to his performance in “Gypsy.”
“He said, ‘I saw you with Ethel Merman, and she was singing to you and spitting all over you,’ ” Mr. Klugman said, recalling Mr. Marshall’s explanation for casting him. “ ‘And you never showed it. That’s a good actor that doesn’t show the spit.’ That’s why he gave me the part"...