!! Emma Becker

Sutton's twin sister and a girl who has moved from foster home to foster home despite being initially adopted by a rich family in Beverly Hills. She switches places with Sutton to escape accusations made by her last foster brother. Is the [[PolarOppositeTwins nicer and more thoughtful twin]].

* AdaptationNameChange: In the books, her name is Emma Paxton.
* CoolBigSis: Is a much better sister than Sutton to Laurel.
* TheHero
* NiceGirl
* FoolishSiblingResponsibleSibling: The Responsible to Sutton's Foolish.
* TheGloriousWarOfSisterlyRivalry: With Sutton.
* PolarOppositeTwins: Is much less outspoken, nicer and generally more thoughtful than Sutton.
* {{Tomboy}}: To Sutton's [[TomboyAndGirlyGirl Girly Girl]].

!! Sutton Mercer

The adopted daughter of the Mercers and Emma's twin sister. She lived happily as a rich girl in Phoenix until she discovered she had a twin after coming home from a trip to Paris, she decides to go to LA and look for their biological mother.

* AllGirlsWantBadBoys: Probably why she dated Ethan.
* AlphaBitch: Played with, she has some of the characteristics (Popular, Manipulative and wants to be Homecoming/Prom Queen) but she doesn't care enough to truly become one.
* BookDumb
* BrilliantButLazy
* TheChessmaster: Sutton was already shown as quite the chessmaster but the season finale revealed that [[spoiler: she was collaborating with her mother Rebecca.]]
* [[spoiler: DisneyDeath]]
* [[spoiler:TheDragon]]
* FoolishSiblingResponsibleSibling: The Foolish to Emma's Responsible.
* TheGloriousWarOfSisterlyRivalry: With Emma and Laurel.
* HeelFaceTurn: She eventually comes to realize Rebecca can't be trusted and decides to help Emma.
* TheLancer
* PolarOppositeTwins: Is more manipulative, outspoken and much meaner than Emma.
* PosthumousCharacter: In the books, she is dead, but her spirit watches over Emma as she tries to figure out who killed her.
* SparedByAdaptation: But She's very much alive in the show.
* [[TomboyAndGirlyGirl Girly Girl]]: To Emma's Tomboy.
* PreppyName
* RichBitch

!! Madeline "Mads" Rybak

* AmbiguouslyBrown: Her actress' heritage is a mess of ethnicities/races.
* BigBrotherWorship: Is very close to Thayer.
* TheChick: [[spoiler: After she finds out the secret.]]
* HotForTeacher: Her dance teacher to be exact, her father was not amused.

!! Thayer Rybak
Alec's son and Mads' older brother. He is keeping the twins' secret and helping them solve their mysteries. Was an UnluckyChildhoodFriend for Sutton but recently developed feelings for Emma.

* DoggedNiceGuy: To Sutton.
* [[spoiler:FaceHeelTurn / EvilAllAlong]]: Which is true, nor his motivations will never be revealed
* FakeGuestStar
* PreppyName
* SecretKeeper
* TheSmartGuy

!! Laurel Mercer

* BetaCouple: With Justin.
* BigSisterWorship
* BigSisterInstinct: To Sutton.
* TheCastShowoff
* CoolLoser: Despite being lovely, intelligent, rich and friendly, she is apparently a nerd and pales in comparison to Sutton.
* TheGloriousWarOfSisterlyRivalry: With Sutton.
* HollywoodNerd: She may be smart, but she's as pretty as everybody else at Arroyo.
* PreppyName

!! Ethan Whitehorse
Sutton's boyfriend who ends up falling in love with Emma.

* TheBigGuy
* HeyItsThatGuy: [[BeverlyHills90210 You may]] [[SwitchedAtBirth remember him]] for playing other bad boy-ish characters.
* RaceLift: In the books, he's the blond-haired, blue-eyed, astronomy-nerd Ethan Landry.
* SecretKeeper
* SiblingTriangle

!! Ted Mercer
Sutton's adoptive father and birth father of Laurel. Is married to Kristin and best friends with Alec. He has several secrets, several revolving around both Annies and Justin.

* [[spoiler: LukeIAmYourFather]]: He didn't know about Emma though.
* PreppyName
* YourCheatingHeart: With [[spoiler: Rebecca]].

!! Kristin Mercer
Sutton's adoptive mother and birth mother of Laurel. Is married to Ted and oblivious of many of his secrets.

* HeroicSafeMode: [[spoiler: In the finale, after Rebecca confirms her fears of her and Ted's affair, she switches to HeroicBSOD when Ted makes his speech at the engagement party]].

!! Alec Rybak
The Phoenix District Attorney and father to Mads and Thayer. Can be controlling and may have some secrets. Is best friends with Ted and beginning a relationship with Rebecca Sewell.

* BigBad
* FakeGuestStar
* PreppyName

!! Annie 'Rebecca' Sewell

* [[spoiler: BigBad]]
* [[spoiler: [[LukeIAmYourFather Sutton And Emma I Am Your Mother]]]]: She only tells Sutton though.
* [[spoiler: ManBehindTheMan]]

!! Char Chamberlain

One of Sutton's TrueCompanions. She's initially suspicious of Emma's actions in Sutton's place, but eventually embraces it as a new direction in their friendship.

* DemotedToExtra
* LockedOutOfTheLoop: Was initially worried about this when her friends started keeping secrets from her, she gets better.
* PutOnABus

!! Nisha Randall

An ex-friend of Sutton's who is technically the series AlphaBitch, she's not as [[AdvertisedExtra profilic]] as her character type is on other shows. She still seems to want to be friends with Sutton and is mean to her as a means to get her back for [[NoodleIncident whatever she did.]]

* AdvertisedExtra
* AlphaBitch
* DemotedToExtra
* RaceLift: In the books, Nisha (whose last name there is Banerjee) is Indian. In the show, she's African-American, with the last name Randall.
* RichBitch

!! Justin Miller

Laurel's first official boyfriend and a golf jock. He pretends to be as wealthy as the other Arroyo but is actually secretly living in a foreclosed home. He tells Laurel that his parents dies years ago in a car crash [[spoiler: but later in series it's revealed he has ulterior motives. ]]

* BecomingTheMask
* BetaCouple: With Laurel
* JerkJock: Averted, he's pretty nice.
* InLoveWithTheMark