How You Know Them:This is Williams' first return to series television since he played a fun-loving alien on Mork and Mindy, but his movie career includes such films as Good Will Hunting, Mrs. Doubtfire and Dead Poets Society. Gellar's iconic role is the titular heroine of Buffy the Vampire Slayer, though she also recently starred (as twins!) on the ill-fated 2011 series Ringer. The New Roles: Williams and Gellar play a father-daughter team who work at an advertising firm. Gellar's used to being a leading lady, but she'll have to settle for more of a supporting role here, thanks to Williams' outsize personality. Look for Williams to employ his typical one-man-comedy-act shtick, with Gellar acting as the straight woman to his frenetic goofiness.

How You Know Him: Where do we begin? Among his many iconic roles, small screen viewers know him best as the yuppie, do-gooder Republican Alex P. Keaton from Family Ties and the intelligent and lovable but romantically challenged Deputy Mayor of New York Mike Flaherty on Spin City. The New Role: After playing the beloved son and the hopeless singleton, Fox will play a married family man with three children. Because his character is an adored New York TV anchor who restarts his career despite his struggle with Parkinson's, Fox's latest character is a surprisingly close reflection on his real life.

How You Know Him: On The Practice and its spin-off Boston Legal, Spader lawyered it up as the highly idealistic yet ethically flexible attorney Alan Shore, a role that won him two Emmys. More recently, he played Robert California, the odd and oversexed CEO of Dunder Mifflin's Scranton branch on NBC's The Office. The New Role: Raymond "Red" Reddington is a mystery man — a formerly on-the-run criminal who has inexplicably turned himself in to the FBI in order to inform on other top criminals. He's smart, he's confident and he's surprisingly in control.

How You Know Them: During his seven-year stint on SNL, Samberg became the go-to cast member for viral musical videos such as "Lazy Sunday," "I'm on a Boat," "D--- in a Box," and so many more. Meanwhile, Braugher earned his stripes (and an Emmy) for playing Detective Frank Pembleton on Homicide: Life on the Street as well as putting in memorable dramatic turns on Men of a Certain Age and Last Resort. The New Roles: Braugher is back on the beat, but this time he goes for laughs as NYPD captain Ray Holt, a no-nonsense veteran who must get his new team, including Samberg's skilled but goofy and immature detective, in order.

How You Know Him: For better (and for worse), Arnett will always be tied to his self-absorbed, immature and womanizing role as Gob Bluth on Arrested Development. He's also recurred on 30 Rock and starred in the short-lived comedy series Running Wilde and Up All Night. The New Role: As a recently divorced local TV personality, his character Jack is much easier to root for than Gob. That's partly because he seems to only want to do right by his two fighting parents, no matter how much they hurt his personal life when they move in with him.

How You Know Him: Hayes won an Emmy and four Screen Actors Guild Awards as over-the-top Cher worshipper Jack McFarland on Will & Grace. He has since done theater, earning a Tony nomination for Promises, Promises, and produces Hot in Cleveland and Grimm. Oh, and he guest-starred as an over-the-top difficult diva on Smash. The New Role: Hayes will still play a flamboyant gay guy — but this time it's not Just Jack. When his titular character's teenage daughter Ellie (Sami Isler) moves in full-time with him, he tries to be the best dad in the world.

How You Know Him: Though best known for his role as Bobby Donnell, the head of the law firm on The Practice, he's also starred in TV series including the short-lived Big Shots, TNT's cop drama Dark Blue, and, most recently, FX's American Horror Story. The New Role: On CBS' political conspiracy thriller, McDermott plays Duncan Carlisle, a rogue FBI agent who takes a surgeon (Toni Collette) and her family hostage the night before she is set to operate on the president.

How You Know Them: Faris played herself on Entourage, but is best known for her big-screen roles in The House Bunny and What's Your Number? Janney starred as the smart, witty press secretary CJ Cregg on The West Wing, but her last starring role on TV was as Matthew Perry's absent-minded boss in the short-lived 2011 series Mr. Sunshine. The New Roles: Faris plays a newly-sober single mom who's trying to get her life together. Janney stars as her mother, who hasn't exactly been the portrait of parental stability and is now trying to reconnect with her daughter and granddaughter. Both roles are tailor-made for the actresses' quirky brand of comedy.

How You Know Them: O'Connell, the erstwhile Vern Tessio in Stand By Me, hasn't had much small screen luck as of late. His CBS drama The Defenders was axed after one season and his Mockingbird Lane pilot was not picked up by NBC. Shalhoub won three Emmys and a Golden Globe as the titular OCD detective on Monk. Kumar Penn shocked us all when his character Dr. Kutner committed suicide on House (so Penn could work at the White House) and he later wooed Robin on How I Met Your Mother. The New Roles: All three play bachelors who befriend a newly single guy Carter (Chris Smith) at their short-term apartment complex. O'Connell plays Stuart, an OB/GYN in the midst of his second divorce who is allergic to shirts. Shalhoub does a total 180 from Adrian Monk as Frank, a four-time divorcee and ladies' man, while Penn plays the mopey, contrite Gil, who got kicked out by his wife after she caught him having an affair and is desperate to win her back.

How You Know Him: Although Gregg recurred on The West Wing and starred on the CBS comedy The New Adventures of Old Christine, he is recently better known for his role in the Marvel superhero films as Agent Coulson, who first appeared in Iron Man and met his demise in The Avengers. The New Role: Coulson lives! Somehow, Gregg will reprise his role as our favorite S.H.I.E.L.D. agent, but it's unclear exactly how he's been resurrected.

How You Know Him: Fans last saw him playing one-half of a dysfunctional (but fun!) detective duo on the short-lived Common Law, but he's also known for his roles on FlashForward and The Good Wife. The New Role: Ealy might become the first actor to want to be described as robotic. That's because on Almost Human, he plays a cyborg cop that's able to understand the emotions of his human partner (Karl Urban) and others.

How You Know Them: Caan is a legend on the big screen thanks to his roles in The Godfather and Misery, but his last gig as a series regular on TV was playing tough casino owner Ed Deline on Las Vegas. Lawson has played the funny and focused Juliet on Psych since 2006. The New Roles: Lawson stars as Terry Gannon Jr., a down-on-her-luck former softball All-Star who moves her son Danny in with her estranged father (Caan), an ex-athlete nicknamed "The Cannon." Caan will dust off his grumpy old man technique (see also: Elf), while Lawson will bring Juliet's sense of fun professionalism to the part as the coach of a team of misfits.

How You Know Him: Most recently, he played reckless, washed-up Detective Dan Stark on The Good Guys. Before that, he brought Aaron Sorkin's words to life as workaholic and former drug addict Danny Tripp on Studio 60 on the Sunset Strip and workaholic deputy chief of staff Josh Lyman on The West Wing. The New Role: Unlike his most famous characters, which were unlucky in love because of their commitment to their careers, Whitford's Trophy Wife character, Brad, is a family man who has been married three times and seems to be at least slightly more adept at juggling his personal and professional lives.

How You Know Him: Green, who played Dr. Evil's son Scott in the Austin Powers franchise, is most familiar to TV fans as the voice of Chris Griffin on Family Guy, as well as several characters on Robot Chicken, American Dad! and other cartoons. The New Role: Green steps into a live-action role as Eli, a thirtysomething video game creator whose life gets turned upside down when his elderly father moves in with him. After dealing with an exasperating father figure like Dr. Evil, we think this new role will fit like a glove.

How You Know Him: The comedian has played Larry David's unscrupulous, adulterous manager Jeff Greene on Curb Your Enthusiasm since the beginning of the series. The New Role: He'll, uh, curb his dubious behavior to play Murray, the hot-headed, gruff but lovable patriarch of the show's titular '80s-era family.

How You Know Him: After rising to fame during a seven-year stint on L.A. Law, Underwood has appeared on such shows as Sex and the City, Dirty Sexy Money and In Treatment. He most recently played the president on NBC's short-lived The Event. The New Role: Underwood plays Robert T. Ironside, the role made famous by Raymond Burr in the original 1960s series. An acerbic police detective who uses a wheelchair after an injury in the line of duty leaves him paralyzed from the waist down, Underwood's Ironside is a rule-breaking cop who'll go to any length to reveal the truth and get justice.

How You Know Her: In a few short years, Wilson has become a household name thanks to her stand-out roles in Bridesmaids and Pitch Perfect as Kristin Wiig's pushy roommate and the outspoken but hilarious Fat Amy, respectively. The New Role: Usually known for playing confident and fun-loving characters, Wilson will take on the meek and nerdy Kimmie, who lacks social skills and prefers to spend her Friday nights hanging out with her friends in pajamas.

How You Know Them: O'Malley broke viewers hearts (in the best way possible) as Kurt's old-fashioned but supportive longtime single father, Burt, on Glee. Meanwhile, Chavira kept viewers' hearts racing as one-half of one of Wisteria Lane's most tumultuous and passionate couples on Desperate Housewives. The New Roles: O'Malley is far less inspiring and tear-inducing as Dan, a father who is excited for his only daughter to go off to college so he and his wife can have more time for themselves and each other (aka sex). As Miguel, Chavira channels Carlos Solis' hot-headed ways but also plays a family man much more invested in being a good father than a good husband.