A Taxonomy of Actors Playing Dual Roles on TV

In the new HBO miniseries I Know This Much Is True, Mark Ruffalo plays the dual roles of Dominick Birdsey and his twin brother Thomas, who is afflicted with paranoid schizophrenia. The miniseries presents Ruffalo with the challenging task of playing twins whose lives have diverged, and whose familial bond is tested by their different circumstances and challenges. Ruffalo, of course, is far from the first to take on a double role. Over the years, TV viewers have seen dozens upon dozens of actors portraying two different characters in both dramas and comedies.

What's constant about TV's double-trouble trope is that it is a veritable buffet for performers to dig into their bag of tricks. It's a chance for them to play darker, funnier, more absurd characters than they're used to, and to flex a number of different muscles on the same project. These performances have taken many different shapes over the years. Below, we've broken them down into the most common categories:

Twins/Doubles as the Central Premise

It's hard to think of actors or actresses playing dual roles on TV and not immediately think of the "identical cousins" of The Patty Duke Show. The 1963-66 sitcom starred the eponymous Patty Duke as bright, charismatic teenage girl Patty and her prim, proper, British-raised cousin Cathy. Coming only two years after the Disney hit The Parent Trap, which got a lot of mileage out of Haley Mills as American/Brit twins, the influence seems obvious. Duke became a big star, and The Patty Duke Show would set the mark for TV shows about twins, even if they weren't exactly twins. The legacy of Patty Duke has been carried on by shows where the central pair of twins are played by actual twins — Sister, Sister; The Suite Life of Zack and Cody — all the way up to modern shows like Living with Yourself, where Paul Rudd plays not twins but clones.

Dark Rivals

This is a hugely popular subgenre of twin TV, and an avenue that is irresistible for actors looking to stretch. These shows present a pair of twins that reside on opposite sides of the same coin. Often one is light and one is dark, but they end up reflecting aspects of each other that they lack or keep hidden in themselves. Most recent examples include Ewan McGregor playing twins Emmett and Ray Stussy -- one happy and successful, one damaged and embittered -- on the third season of Fargo; James Franco as mob-connected twins Vincent and Frankie who get caught up in the porn business in The Deuce; and Yael Grobglas as scheming Petra and her more overtly criminal twin Anezka on Jane the Virgin.

Evil Twins/Alternate Universes

An offshoot of the twin as a dark rival is the tried-and-true "evil twin" storyline. This has been predominantly been used as a temporary storyline — often kept to a single episode — rather than a premise for a show itself. For many this trope is best exemplified by Star Trek, where Spock (Leonard Nimoy) encountered his evil, goateed twin from an alternate dimension. This kind of villainous doppelganger storyline has also appeared in comedies like Gilligan's Island, I Dream of Jeannie, and Bewitched (with brunettes standing opposite their virtuous blonde counterparts), and was later parodied on South Park. On Buffy the Vampire Slayer, a one-episode crossover with an alternate dimension brought Willow (Alysson Hannigan) face to face with her vampire doppelganger. In another alternate universe, on Fringe, Olivia (Anna Torv) and Walter (John Noble) had alternate versions of themselves in a mirror universe that the fans dubbed "Fauxlivia" and "Walternate." More recently, on Pretty Little Liars, Troian Bellisario's Spencer was faced with her own evil twin Alex, who went by A.D. and tormented the Liars throughout Season 7.

Soap Operas

The roots of many of TV's dramatic twin tropes lie in soap operas, which have been trading in these kinds of storylines for years. Pretty much every soap has indulged in a twin storyline at some point. On some shows, twins are around for the long haul, and often played by future stars like Julianne Moore — who played Frannie Hughes and her (British!) twin Sabrina on As the World Turns — and Anne Heche, who played angelic Marley and scheming Vicky Hudson on Another World. The soaps often went heavy on the good twin/bad twin dichotomy, with the likes of ruthless millionaire Adam Chandler and his simple brother Stuart (David Canary) in All My Children and good doctor Kevin Collins and his homicidal twin Ryan Chamberlain (Jon Lidstrom) on General Hospital. Former Real Housewives of Beverly Hills star Eileen Davidson got to turn up the camp factor on the twin trop on Days of Our Lives, playing devious Kristen DiMera and also her unfortunately-toothed, Elvis-obsessed doppelganger Susan Banks.

Ancestry Dot Com

Sometimes the shows get cheeky and cast the same actor in two roles across vast time periods in order to make a thematic point and/or let the actor or actress chew some period-appropriate scenery. Think of the dual roles Tobias Menzies plays across the vast time periods in Outlander. Or how Nina Dobrev played main protagonist Elena and also ancient vampire antagonist Katherine on The Vampire Diaries.

Whoops! We Want to Keep That Actor

Oftentimes, a show will write off a character or have them meet their end as storylines dictate, but they'll want to keep working with the actor, so they have them stick around to play the original character's twin or doppelganger. Perhaps the most famous example of this is when Twin Peaks got so much mileage out of Sheryl Lee as Laura Palmer that they cast her as Laura's cousin Maddy Ferguson. On Heroes, Niki Sanders, the super-powered multiple-personality hero sacrificed herself to save another character at the end of the second season. But in Season Three, the show brought actress Ali Larter back as lookalike Tracy Strauss (who was later revealed as Niki's triplet, obviously). Other examples range from shows like the Melrose Place spinoff Models, Inc. (which killed off Stephanie Romanov in the pilot episode, then kept her on as inexplicable doppelganger "Monique") and Scrubs (which wrote off Aloma Wright's Nurse Laverne, and then after the show was unexpectedly renewed, brought Wright back as Nurse Shirley). And we can't forget Penny Dreadful's Patti LuPone for playing a rural abortionist, then returned the next season to play a psychologist for multiple episodes.

Just for Laughs

Some of the best and most memorable examples of dual casting come from sitcoms using the gambit for laughs. Most notable among these has got to be Friends importing the waitress Ursula from Mad About You to be the twin sister of Lisa Kudrow's Phoebe. Friends also did a one-off gag where David Schwimmer played the sad-sack Ross lookalike named Russ. There's also Jeffrey Tambor playing both unscrupulous businessman George Bluth as well as his hippie twin brother Oscar on Arrested Development. Most recently, Ken Marino has played twin financiers Larry and Lenny Leighman, who have been the butt of incest jokes and freak accidents on Showtime's Black Monday.

Multiple Copies

And then there are the shows that don't do twins as much as clones, which really allows actors show their stuff. Tatiana Maslany won an Emmy award for playing the many different clones on Orphan Black. Battlestar Galactica's many-copied Cylons gave the likes of Grace Park, Tricia Helfer, and Lucy Lawless the chance to impress by playing vastly different personalities. Similarly, Darcy Carden earned rave reviews for playing the various Janets on The Good Place.

Will Mark Ruffalo earn similar raves for his dual dramatics on I Know This Much Is True? It's very likely, given his pedigree as an actor. Whatever happens, he's now joined a proud television tradition. Anything that binds Gilligan's Island to Battlestar Galactica is a formidable TV trope indeed.

Joe Reid is the senior writer at Primetimer and co-host of the This Had Oscar Buzz podcast. His work has appeared in Decider, NPR, HuffPost, The Atlantic, Slate, Polygon, Vanity Fair, Vulture, The A.V. Club and more.