Osmosis "Ozzy" Jones
Voiced by: Chris Rock
- Cheshire Cat Grin: He sports one of these every now and again.
- Cool Car: Had his cop car customized.
- Cowboy Cop
- Dogged Nice Guy: Has trouble winning Leah Estrogen's affections. He does at the end, though.
- The Hero
- In-Series Nickname: Always known by "Ozzy".
- Nice Job Breaking It, Hero: He did the right thing causing Frank to vomit, thereby saving him from a contaminated oyster, but it caused Frank to lose his job and the respect of the local community, and got Ozzy suspended for "use of unnecessary force".
- Official Couple: With Leah at the movie's end.
- Protagonist Title
- Red Oni, Blue Oni: The red to Drix's blue.
- Sensitive Guy and Manly Man: The Manly Man to Drix's Sensitive Guy.
- Sesquipedalian Smith
- Shapeshifter Showdown: What saves him against Thrax.
Voiced by: David Hyde Pierce
- Arm Cannon
- The Big Guy
- But Not Too White: Drix is played by David Hyde Pierce. The producers were looking for someone as white-bread as possible. Niles Crane is about as white-bread as you can get.
- By-the-Book Cop: Part of what makes him different from Osmosis.
- Captain Ersatz: Drix bears a strong resemblance to Iron Man.
- Genius Bruiser
- An Ice Person: His painkilling abilities are portrayed as this.
- In-Series Nickname: "Drix" is this, short for Drixenol (or Drixobenzometaphedramine).
- The Lancer
- Red Is Heroic: His main colors are red and yellow.
- Red Oni, Blue Oni: The blue to Ozzy's red.
- Sensitive Guy and Manly Man: The Sensitive Guy to Ozzy's Manly Man.
- The Smart Guy: He certainly acts smarter than Osmosis, at least.
Voiced by: Laurence Fishburne
- Ass Kicking Equals Authority: He gets the bacterias to accept him as their leader after he single-handedly killed their boss.
- Badass Longcoat: One he can even use as a glider.
- Berserk Button: Do not get in the way of his goal of being in the medical books. He killed all of his men when one suggests they incubate.
- Big Bad: He's the reason why Frank is in danger.
- Cool Shades: Owns a pair of these, and wears them frequently.
- Deadpan Snarker
- Diseased Name: And a Punny Name at that, as his name is a play on the bacteria anthrax. Justified, since he's a bacteria.
- Establishing Character Moment: The first thing he does upon being introduced is to casually murder two harmless workers, at least one in an incredibly gruesome way. He then proceeds to burn their entire boat by merely scratching its surface with his index while he is walking.
- Even Evil Has Standards: Is visibly disturbed upon seeing some of Frank's nightmares and bad memories.Thrax: (after escaping from the room) This cat was sick before I even got here!
- Evil Is Petty: Only partially. Thrax wants to kill Frank in a record time so he can be in medical textbooks.
- Family-Unfriendly Death: He falls into a vat of alcohol, which of course has very deadly effects on germs... although to be fair this tends to be how irredeemable villains tend to die...
- Also applies to the first cell he kills. What he does to the bacteria mob boss too, though to a lesser degree.
- Faux Affably Evil: He likes to hum "Fever" by Peggy Lee and presents himself as charismatic, but this barely hides the monster he is.
- Finger Poke of Doom: Quite literally with his first victim. "Ouch."
- Glory Hound: Thrax is like a serial killer who's trying to become famous in the most brutal fashion.
- Playing with Fire: His fingernail claw burns whatever he scratches into a melting, burning lava mess.
- Knight of Cerebus: Were you expecting a movie about Chris Rock as a blood cell to have a virus in the form of a serial killer?
- Names to Run Away from Really Fast: Thrax, meant to evoke anthrax.
- Nice Job Fixing It, Villain: In the final battle with Ozzy, he use the black chain holding the hypothalamus chromosome to try and choke him. But then Shane blinks, separating the two with the chain still around Ozzy's neck. His final attack failing thanks to Ozzy's morphing abilities seal the deal.
- Omnicidal Maniac: Thrax's plans involve killing people, causing the civilizations of cells in their bodies to die. The loss of life is apocalyptic at the cellular level, with an implied decimation among humans (since Thrax wants his own chapter in the medical books he'd likely seek to become an epidemic, which would entail massive loss of life).
- Red and Black and Evil All Over: Red-skinned, dressed in black, and definitely evil.
- Scary Black Man: Only in voice (Laurence Fishburne does it).
- Serial Killer: He keeps trophies from his victims and reminisces about them.
- A Sinister Clue: Only a given, since that's the hand he uses to kill all his victims and spread his infection.
- Slasher Smile: He sports quite a few throughout the movie, the most notable one being when he threatens to kill Frank's daughter.
- Soft-Spoken Sadist: He likes to keep a low tone at times.
- Vile Villain, Saccharine Show: And how. Apart from the serial killer overtones, there's his meeting the group of germs in the Zit. With the plan to organize coordinated assaults with the intention of causing widespread death and destruction, also spreading fear and intimidation outside Frank, Thrax comes across as a leader of a terrorist group planning an attack. It's jarring how such a vicious, murdering villain managed to stick in an otherwise light-hearted comedy.
- Villainous Cheekbones: Thrax's cheekbones are so pointy they look sharp, and he his clearly evil.
- Touch of Death: His left index finger causes any organic matter it touches to combust or explode.
- Would Hurt a Child: Brags about killing a little girl - and has his sights on Frank's daughter when he's done with Frank.
Voiced by: William Shatner
- Fat Idiot: He clearly doesn't see what could happen if he keeps giving Frank junk food instead of healthy food, hence the obesity.
- Hate Sink: As he is designed to represent and justify Frank's poor health, he inevitably ventures into this. Notably, he abolishes Ozzy from the police force for making Frank throw up even though it was an emergency situation, fails to acknowledge Thrax as a threat despite the fact that he had killed others in the past (dismissing him as the common cold when he was one of the deadliest viruses ever), and is the only one that doesn't see the problem in giving Frank nothing but junk food.
- Jerkass : He certainly is, especially to Ozzy.
- Laser-Guided Karma: Abolished Ozzy for having Frank throw up to get out an evil virus. Then at the end when he's been booted out of office, he presses a similar button and winds up flushing himself right out of Frank's own body.
- Mayor Pain: Though he's not corrupt per se, he's VERY incompetent at his job and cares more about his election than anything else.
- My God, What Have I Done?: Doesn't say it but his reaction as the city of Frank burns down around him pretty much has this trope all over it.
- Obstructive Bureaucrat: Let's see, he fired Osmosis and gets Drix out of Frank just for popping a pimple without permit (Which is like blowing up a building in the real world) and as mayor control's nearly all of Frank's actions, including his slovenly behavior. Said neglect needless to say, almost ends up killing the guy and every cell with him.
- Sleazy Politician: To the tee.
- Too Dumb to Live: His actions almost get his city destroyed.
Voiced by: Brandy Norwood
- The Chick
- Graceful Ladies Like Purple: Her suit and even her body are both purple.
- Living MacGuffin: Is taken hostage by Thrax, and very nearly killed by him.
- Non-Mammal Mammaries
- Office Lady: Works as a secretary for Mayor Phlegming.
- Official Couple: With Ozzy in the end.
- Sassy Black Woman
- She's Got Legs: That mini-skirt isn't helping the fact that she has long legs.
- The Smurfette Principle: Although Leah isn't the only female anthropomorphic cell in Frank's body, she's the only one with Nominal Importance.
- Tsundere: Type B.
- Women Are Wiser
Francis "Frank" DiTorre
Played by: Bill Murray
- Bumbling Dad: He means well, and does care about Shane, but he has a major selfish streak. Though this is mostly due to Mayor Phlemming overriding his body for his own ends.
- Children Raise You
- "Fantastic Voyage" Plot: The plot takes place inside Frank's body
- Fat Idiot
- Guys Are Slobs: Played straight and subverted, as in a flashback we hear Shane complain that neither he or Maggie, his wife, take care of themselves very well, Frank just got worse after Maggie died.
- The Mourning After: Still mourning the loss of his wife, Maggie. Justified, as it seems to be a relatively recent loss.
- One of the Kids
- Straw Loser
- Too Dumb to Live: What kicks off the whole plot as he eats an egg that was inside the mouth of a monkey and got spat out onto the ground. Yeah that seems sanitary.
- Vomit Indiscretion Shot: Double Subverted; we don't see it actually happen (although we hear him retching, the focus is on the horrified crowd at the science fair), but we do see a picture of him puking all over Shane's teacher.
Played by: Elena Franklin
- Broken Bird
- Calling the Old Man Out: Blames Frank and his unhealthy habits for Maggie's untimely death, and calls him out for deciding to take her to a chicken wing Fan Convention instead of the hiking trip she was looking forward to.
- Children Raise You: Takes care of her dad, because he doesn't take care of himself.
- Gender-Blender Name: Her first name is predominantly used by boys.
- Missing Mom: Her mom died of an unspecified illness. Though it's implied she was as unhealthy as Frank has been throughout the movie.
- Only Sane Woman: Shane often has to be the adult between her and her father.
- Women Are Wiser