->'''Played By:''' Jason Ritter
* ActionSurvivor -> ActionHero
* AntiHero: Type III
* BreakTheCutie: [[spoiler:After leaving Leila.]]
* [[spoiler: TheChosenOne]]: Dempsey seems to think he's this, in regards to the threat of Sophia's people.
* PlayfulHacker: In his youth. He still has some connections.
->'''Played by:''' Sarah Roemer
* DamselInDistress -> ActionSurvivor
* IdiotBall: [[DesignatedVictim She is always]] [[DamselInDistress captured and needs Sean to rescue her.]] Even though it seemed as if she TookALevelInBadass recently, her forays into heroism are far less successful than Sean's. [[spoiler: When she is escaping with Michael and Simon, she decides to stay at her (presumably) dying father's side instead of leaving with Simon to go where she might actually help.]]
* [[spoiler: HalfHumanHybrid]]
* [[spoiler: TomatoInTheMirror: Had absolutely no clue her dad was an alien.]]
->'''Played By:''' Scott Patterson
* [[spoiler: AlienAmongUs]]
* [[spoiler: InterspeciesRomance: Complete with two kids.]]
->'''Played By:''' Taylor Cole
* ActionMom: Adopted a baby whose family she killed for the job.
* AntiVillain [[spoiler:-> AntiHero (Type IV)]]
* BreakoutCharacter: Because of her popularity with viewers, her role increased as the series went on. By the end the series, she had effectively replaced Leila as the female lead.
* DarkActionGirl: [[spoiler:Before her HeelFaceTurn.]]
* EvenEvilHasStandards: Turned against Dempsey after finding out about his experiments on girls.
* [[spoiler: HeelFaceTurn]]
->'''Played By:''' Blair Underwood
* OurPresidentsAreDifferent: President Minority, starts off as President Personable [[spoiler: and soon turns into President Iron when dealing with Sophia, and quite possibly President Evil depending on how you view things.]]
* TranquilFury: See Episode 15.
->'''Played By:''' Zeljko Ivanek
* MadeOfIron: [[spoiler: Took a bullet, kept walking around for a good long while, got tortured, stayed stable, got shot ''again'' and was still able to crawl around a bit.]]
* CharacterDevelopment: Starts out looking like he's going to be a KnightTemplar, but turns out to be a truly good guy.
->'''Played By:''' Bill Smitrovich
* OurPresidentsAreDifferent: Well, ''Vice'' Presidents; [[spoiler:he's Vice President Scheming, even being involved in the attempted assassination on Martinez.]]
** [[spoiler: Two of them, actually. He's agreed to help Sophia take out Martinez, both so that he can [[DealWithTheDevil become President and to protect America from the impending invasion]].]]
* UnwittingPawn: To Dempsey, partially. And now even more so to [[spoiler: Sophia]].
* WellIntentionedExtremist: Everything he does, [[spoiler: including the attempts on the President's life,]] has been to protect his country.
** [[spoiler: [[SubvertedTrope Although it's peculiar just how many of the actions he takes "in service to his country" also happen to benefit him personally. Indeed, Sophia partly plays on his ego, painting a picture of him as "the man who saved America" while getting him on her side.]]]]
->'''Played By:''' Lisa Vidal
* DemotedToExtra: In the main cast, yet we barely ever seen her.
->'''Played By:''' Laura Innes
* [[spoiler: HazyFeelTurn: After Thomas' death.]]
->'''Played By:''' Clifton Collins Jr.
* BigBadWannabe: And he was succeeding, for awhile.
* [[spoiler: HeroicSacrifice]]
** [[spoiler: DeathEqualsRedemption]]
* WellIntentionedExtremist: Well, [[spoiler:his entire race is gonna die unless they find a new home planet. He's kind of got a reason to want to get things going.]]
->'''Played By:''' Ian Anthony Dale
* DefectorFromDecadence: After [[spoiler:Sophia's HazyFeelTurn.]]
* InterspeciesRomance: Was in love with a human girl, but Thomas convinced him to leave her. Years later he ran into her, now an elderly woman, himself looking exactly the same.
* TheMole: An Alien working in the White House.
->'''Played By:''' Hal Holbrook
* AncientTradition: Claims to part of a tribe of "Sentinels" who have protected Earth from the aliens for thousands of years.
* BigBad: Starting to look like it...
** At least until [[spoiler: he kills himself]].
* [[spoiler: DroppedABridgeOnHim]]
* WellIntentionedExtremist: Justifies his actions by saying it's to stop the impending AlienInvasion.
!!Agent Angela Collier
->'''Played By:''' Heather [=McComb=].
* [[CIAEvilFBIGood FBI Good]]
* WhatHappenedToTheMouse: Nothing comes of her entire FBI field office getting slaughtered by [[spoiler: Dempsey's conspiracy.]]
->'''Played By:''' Necar Zadegan
* BigBadWannabe: With Thomas.
->'''Played By:''' D. B. Sweeny
* MauveShirt: Considering it's a wonder he's even got a name...
->'''Played By:''' Clea [=DuVall=]
* CradlingYourKill: After killing her boyfriend, who was going to give information about Sophia to the government in exchange for releasing them from Inostranka.
* [[spoiler: HeroicSacrifice: Via...]]
** [[spoiler: TakingTheBullet: For Sterling.]]
** [[spoiler: RedemptionEqualsDeath]]
->'''Played By:''' Creator/VirginiaMadsen
* NoCelebritiesWereHarmed: A feisty female [[strike: Governor]] Senator from Alaska? [[UsefulNotes/SarahPalin Hm.]]