Big-name guest stars popped up on the show (Sammy Davis, Jr., Troy Donahue, Peter Lawford, and Sal Mineo, just to name a few), and Duke even earned an Emmy nomination for her roles on the Sidney Sheldon-created series.
But the show's star definitely played favorites. Five decades after her TV twin debut (OK, they were cousins, but they were "identical cousins"), Duke told the Los Angeles Times, "I liked Cathy better. Patty was very embarrassing to me. They would write those outrageous things for her to do. I would dive in and do it, but I couldn't wait to get to Cathy. She was sensible, and I'd like to think she was classy."
Check out "The Patty Duke Show" opening and closing themes:
Of course, over the past 50 years, TV twins have come and gone, but has any duo lived up to the Emmy-nominated Patty and Cathy? Or could it be that when they made those identical cousins, they broke the mold?
In 2011, Sarah Michelle Gellar was a dead ringer -- for herself. The CW series "Ringer" starred the former "Buffy the Vampire Slayer" actress as identical twin sisters Bridget and Siobhan. (Talk about troubled twins: One of them witnessed a murder while her sis had a bounty on her life.)
At the time, Gellar told Entertainment Weekly, "Bringing to life two characters and making them different, but at the same time interesting, and [showing] the similarities is definitely a challenge I've never done."
She also added that she loved the surprise element of the show: "Usually I see it coming, and I didn't see ['Ringer's' plot twists] coming." The actress also didn't see the show's demise coming: "Ringer" was axed after a single season. But at least it gave us double the Gellar for a little while.
On the NBC comedy "Friends," Lisa Kudrow famously played Phoebe Buffay, but she also played Pheebs's identical twin sis, Ursula. But in a twin twist, Ursula also did double duty as a recurring character on NBC's "Mad About You."
In an interview with Archive of American Television, Kudrow explained how the Ursula crossover came about: "When 'Friends' got its time slot after 'Mad About You,' then I think they needed to start discussing… [why] you're seeing the same girl, the same voice at 8 and 8:30 on two different shows," she said. She joked that the Buffay twins were "two versions of different idiots."
Watch a montage of Phoebe and Ursula clips from "Friends":
Of course, sometimes the roles of twins go to, well, twins. Tia Landry and Tamera Campbell famously played polar opposite twins on the sitcom "Sister Sister," while Dylan and Cole Sprouse played hotel-dwelling identicals Zach and Cody Martin on "The Suite Life of Zach and Cody."
And in the late 1980s, the ABC sitcom "Full House" housed two sets of twins, but only one set of sibs played twins on TV. While Mary-Kate and Ashley Olsen shared the role of Michelle Tanner on the series, real-life twins Blake and Dylan Tuomy-Wilhoit played Uncle Jesse and Aunt Becky's cutie patootie twin boys, Nicky and Alex. So, yes, one set of twins shared one role and a second set of twins played two roles. (And yes, it's confusing!)
In 2009, Mary-Kate told Interview Magazine that the sisters' scenes on "Full House" were decided by "who wouldn't cry in front of the camera." She also said their reward for nailing a scene was "little gummy bears cut into three pieces."
While the sisters didn't play twins on "Full House," they did play the part off-camera: "If my sister and I did an appearance, we would be wearing the same outfit," Olsen said of their tween days. "It would be the same dress, and we'd fight over who would wear it in red and who would wear it in black."
But by that time, they really did play twins on TV. In the late '90s, the Olsens starred as twin sisters on the shows "Two of a Kind" and "So Little Time."
Watch the Olsen twins confuse us even more when they trade places on "Two of a Kind":
Up next: The Disney Channel will debut "Liv and Maddie," which stars Dove Cameron as identical twin sisters who reunite after one of them returns from Hollywood after starring in a hit TV musical. Disney's VP of original programming, Adam Bonnett, told Variety, "We've challenged one very talented teen with the opportunity to play two sitcom roles simultaneously, and we're confident that she will continue our track record of presenting relatable characters and comedic stories for a generation of kids and families."
"Liv and Maddie" premieres on Sunday, Sept. 15 at 8 p.m. on the Disney Channel.
More from this contributor:
- Arts & Entertainment
- Patty Duke
- Patty Duke Show
- Sarah Michelle Gellar