On September 19, Ashton Kutcher debuts in the sitcom, playing an Internet billionaire. The final nail in Charlie Sheen’s coffin? The first episode reportedly opens at his character’s funeral—after he was hit and killed by a train. Ouch!

After a back injury forced Dick York to quit the show, actor Dick Sargent took over the role until the show ended in 1972. The case of the “Two Darrins” remains one of TV’s most famous switcheroos.

Luckily, when Farrah Fawcett's character, Jill Munroe, decided to leave and become a racecar driver, she had an equally blonde and beautiful sister to fill her shoes. Cheryl Ladd took over as the third Angel, playing younger sis Kris Munroe for the remaining four seasons of Charlie's Angels.

Sarah Chalke (later of Scrubs fame) stepped into Becky Connor's shoes for seasons six and seven of Roseanne. When Lecy Goranson’s schedule allowed her to return to the show for season eight, the cast handled her reappearance with typical humor. During the first episode Goranson was back, her character was repeatedly asked, “Where the hell have you been?” by the rest of the Connor clan.

Starting in the third season of Batman, the sultry Eartha Kitt stepped into Catwoman's paws. On the big screen, Lee Meriwether, Michelle Pfeiffer and Halle Berry have all portrayed the famous feline. Next to slip into the catsuit? Anne Hathaway in The Dark Knight Rises.

After weeks of public feuding (and the memorable “I’m With Coco” campaign), Conan O’Brien gave up the Tonight Show gig—and reportedly walked away with $33 million. He now hosts Conan for TBS, while Jay Leno is back in his old seat on the Tonight Show—a curious case of the replaced becoming the replacement!

Geri Reischl slipped into Jan Brady's groovy clothes, playing her on The Brady Bunch Variety Hour. Dubbed “Fake Jan” by rabid Brady fans, Reischl and the rest of the cast were put out of their misery when the variety show ended after one year in 1977. Reischl has a sense of humor about the switch: She hosts a "Fake Jan" site and even celebrates an annual "Fake Jan Day"—when people dress as their favorite fakes—with fans.

Jimmy Smits joined the force in David Caruso's place, playing Det. Bobby Simone for the next decade. Caruso’s career didn’t recover until 2002 when he landed on CSI: Miami.

Proving the show can go on with or without its namesake, the sitcom was simply retitled The Hogan Family. Actress Sandy Duncan took Valerie Harper’s place, playing the kids’ aunt, who steps in to care for them after their mom dies in a car crash—yikes!

Diehard fans of the Partridges had a hard time getting happy when the show's second season opened with a new Chris Partridge. But actor Brian Forster remained in place until The Partridge Family ended in 1974.

After the third season of The Fresh Prince of Bel Air, actress Daphne Reed took over as Will Smith's sassy Aunt Viv. The show went on for three more years before being canceled in 1996.

When Shelley Long left Cheers, Kirstie Alley took over as Sam’s new foil Rebecca Howe. Long did return, however, for the series finale in 1993.

After Shannen Doherty left, Tiffani-Amber Thiessen moved into the 90210 zip code as troublemaker Valerie Malone—even moving into Brenda Walsh's old bedroom and dating her former love, Dylan McKay (Luke Perry).

After Michael J. Fox left, Charlie Sheen was elected to take office as new Deputy Mayor Charlie Crawford. So before he was the replaced (on Two and a Half Men), Sheen was the replacement!

It was no surprise when Lisa Ling was brought in to replace the much-lampooned Debbie Matenopoulos in 1999. When Ling left in 2002, Elisabeth Hasselbeck joined The View's roundtable and has remained ever since. Ling now hosts the documentary show Our America on the Oprah Winfrey Network.

Idol proved indestructible: Jennifer Lopez and Aerosmith’s Steven Tyler joined Randy Jackson on the judging panel for Season 10 and viewership increased. As for Simon Cowell, he’ll reunite with fellow former Idol judge Paula Abdul when his new show, The X Factor, debuts on September 21. 

Supporting actress Jasmine Guy (playing southern belle Whitley Gilbert) became the star of A Different World until it ended in 1993.

Comedian Drew Carey took over as host, continuing animal activist Bob Barker’s signature sign-off, which asks viewers to have pets spayed or neutered.

Vanessa Williams happily moved into Edie Britt's house on Wisteria Lane in 2010 and will stay through the end of Desperate Housewives in 2012.

In 2001, soap star Kelly Ripa took over as co-host and the show was renamed Live with Regis and Kelly. Since then, ratings have reportedly gone up. But Live faces a bigger challenge now: Regis Philbin is scheduled to retire in November 2011.

Want MORE? Check out our interview with Octavia Spencer of The Help.

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