The opening credits to The Odd Couple laid out the concept in a simple premise: "Can two divorced men share an apartment without driving each other crazy?"

That question was answered - usually, "No" - 114 times across five seasons on ABC beginning Sept. 24, 1970, as neat freak Felix Unger (Tony Randall) tried to live with his friend, messy sportswriter Oscar Madison (Jack Klugman), after the disintegration of their respective marriages. Although divorce was rare at the time - only 3.2 out of every 1,000 marriages in 1969 ended in a split, but that number had risen a full percentage point during the '60s - the adventures of Felix and Oscar resonated with audiences in its two earlier iterations.

Neil Simon wrote The Odd Couple as a play, which premiered on Broadway in 1965 with Walter Matthau as Oscar and Art Carney as Felix. It won four Tony Awards, including one for Matthau as Best Actor, and ran for 964 performances over more than two years. A film version, with Matthau reprising his role but with good friend and frequent co-star Jack Lemmon as Felix, arrived in 1968. It was a commercial and critical smash, too.

For the TV adaptation produced by Garry Marshall, Randall was cast first, and he lobbied for Mickey Rooney to star opposite him. But Marshall was set on Klugman, who had taken over for Matthau on Broadway eight months into its run. There were a few minor changes to the main characters' backstories: Felix's profession was switched from TV news writer to commercial photographer - "Portraits a specialty," he'd always add - and Oscar was now childless.

Watch the Opening Credits of 'The Odd Couple'

That first season retained the apartment from the movie, as well as the mismatched pair's giggly British neighbors the Pigeon Sisters, Cecily (Monica Evans) and Gwendolyn (Carole Shelley), whom they occasionally dated. But Klugman and Randall, both veterans of the stage, objected to the laugh track, even going on talk shows to ask fans to write the network about it. For Season Two, the laugh track was removed and the show was given a set better suited to a three-camera shoot in front of a live studio audience.

After appearing four times in the first 10 episodes, the Pigeon Sisters gave way to other women. Oscar soon met Dr. Nancy Cunningham (Joan Hotchkis); in the third season, Felix met Miriam Welby (Elinor Donahue). Audiences also got to know their respective ex-wives: Blanche Madison (Brett Somers, Klugman's real-life wife, although they divorced during the series' run) and Gloria Unger (Janis Hansen) whom, despite the frequent presence of Miriam, Felix never fully got over.

While Oscar retained his gruff-but-lovable personality under Klugman, Randall incorporated his love of the arts into his portrayal  of Felix. This not only widened the chasm between the characters, but also offered plenty of opportunities for stunt casting. During its run, the show provided opportunities for guest stars from the worlds of opera (Marilyn Horne, Martina Arroyo and Richard Fredricks) and ballet (Edward Vilella) to show off their talents to a prime-time audience. Oscar's career brought athletes like football players Deacon Jones and Bubba Smith, and tennis stars Billie Jean King and Bobby Riggs onto the set. ABC also occasionally cross-promoted the sitcom with established shows on the network, including Monday Night Football, Password and Let's Make a Deal.

In between all that, Felix and Oscar got on each others' nerves, but they stayed together because they needed one another. Felix's life was in free-fall until Oscar allowed him to share his apartment; Felix's housekeeping and culinary skills brought stability to Oscar's otherwise shambolic life.

Watch the Final Scene of 'The Odd Couple'

Despite the frequent guest stars and the undeniable chemistry of the stars - both men were nominated for Emmys every year of the series' run; Klugman won twice, Randall once - The Odd Couple struggled in the ratings. Perhaps this was because it was mostly shown on Fridays, a night better suited for family comedies than shows centered on adults. Still, it performed better in summer reruns and was brought back four times.

The fifth season concluded on a happy note, with Felix and Gloria remarrying, and the show lived on in syndication and several reboots. The New Odd Couple brought in a pair of African-American actors, Ron Glass and Demond Wilson (as Felix and Oscar, respectively), but it lasted only 13 episodes from 1982-83. In 2015, Matthew Perry helped bring The Odd Couple back to the small screen, starring as Oscar opposite Thomas Lennon's Felix for 38 episodes across three seasons.

Watch Tony Randall and Jack Klugman in a Commercial for Eagle Snacks

Onstage, Simon adapted his play in 1985 for an all-female cast, with Rita Moreno as Florence and Sally Struthers as Olive. He also brought Lemmon and Matthau back in 1998 for a new script called The Odd Couple II.

But it was Randall and Klugman who defined Felix Unger and Oscar Madison. The actors appeared in commercials together and revived their characters in the mid-'90s - first for a new Simon creation, The Odd Couple: Together Again, followed by a tour of the play to seven cities as a benefit for Randall's National Actors Theatre.

A couple of years after Randall's 2004 death, Klugman wrote a book about his friend called Tony and Me.


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