Voiced by: Vanessa Paradis
- Angelic Beauty: While she's not a real angel, Lucille's stage costume was made with this in mind.
- The Chanteuse
- Childhood Friend Romance: With Raoul.
- Deadpan Snarker: Lucille has her moments.
- Fiery Redhead
- Hartman Hips
- Huge Guy, Tiny Girl: With Francœur.
- Like Brother and Sister: With Francœur, according to Word Of God.
- Redheaded Heroine
- Significant Green-Eyed Redhead
- Spirited Young Lady
- Unlimited Wardrobe
- Woman in White: As part of her stage costume.
- Youthful Freckles
Voiced by: Matthieu Chedid (French singing voice), Sean Lennon (English singing voice)
- Amplified Animal Aptitude
- Big Creepy-Crawlies: Francœur is a giant (albeit anthropomorphic) flea.
- Coat, Hat, Mask
- Cool Mask
- Cute Monster
- Cute Mute: He can only "speak" in chirps and bleeps, but nobody cares because of how ridiculously cute it is. Did we mention he can sing, too?
- Gentle Giant
- The Grotesque: He's a sweet-natured, kind, passionate seven-foot-tall flea. The number that shares the film's title is about how no-one (up to that point) can manage to see past his terrifying, monstrous exterior long enough to see his true nature, and how he's forced to hide himself because of it.
- Huge Guy, Tiny Girl: With Lucille.
- Immune to Bullets: Francœur takes a couple shots to the exoskeleton without batting an eye.
- In a Single Bound: Justified since he's a flea.
- Instant Expert: Francœur learns to sing, dance and play guitar damn fast. He's later seen writing a piano piece!
- Like Brother and Sister: With Lucille, according to Word Of God.
- Line-of-Sight Name: Francœur gets his name from a sign in the alley where Lucille finds him.
- Man in White
- Meaningful Name: Francœur means "honest heart".
- Nice Hat
- The Speechless: Francœur, outside of the songs, is incapable of speaking and chirps (or sings basic sounds) instead, which makes him even cuter. The set-up for A Monster in Paris (the song) implies he needs to hear music of any sort to be able to talk/sing.
- Tiny-Headed Behemoth
- Vocal Dissonance: Let's be honest, nobody expects a 7-foot-tall flea monster to have such a high-pitched voice.
- White Gloves
Voiced by: Gad Elmaleh (French), Adam Goldberg (English)
- Adorkable: Tall, clumsy, and filled to the brim with stupid jokes.
- Childhood Friend Romance: With Lucille.
- Deadpan Snarker
- Gadgeteer Genius: He invented and operates his Cool Car, Catherine.
- Heroes Want Redheads: Raoul has a big thing for Lucille.
- Jerk with a Heart of Gold
Voiced by: Sébastien Desjours (French), Jay Harrington (English)
- Decoy Protagonist: The movie starts out following him and Raoul, but the focus shifts over to Francoeur and Lucille.
- Little People Are Surreal: Averted. While Emile is technically a little person, the film treats this characteristic with sensitivity, touching on how this impacts his self-esteem.
- Shrinking Violet
- Took a Level in Badass: Emile directly fights Maynott and wins by using his wits!
Voiced by: François Cluzet (French), Danny Huston (English)
- Big Bad
- Cool and Unusual Punishment: His final fate.
- Captain Ersatz: Has a lot of similarities with Gaston.
- He Who Fights Monsters
- It's All About Me
- Punny Name: If he won the election, he would be Mayor Maynott
- Sharp-Dressed Man
- Villainous Crush: It's obvious he's eager to have Lucille as a Trophy Wife.
Voiced by: Philippe Peythieu (French), Bob Balaban (English)
- The Dragon
- Fair Cop
- Heel-Face Turn
- To Be Lawful or Good: Paté is confronted to this choice as he realizes that Maynott is a bastard and is completely losing his sanity. He chooses the second option.
- Token Good Teammate
Voiced by: Ludivine Sagnier (French), Madeline Zima (English)
- Graceful Ladies Like Purple
- Love Interest: To Emile.
- Proper Lady: She is soft-spoken, polite and has a gentle strength, contrasting the feisty and spirited Lucille
- Smooch of Victory: Gives Emile a BIG one after he defeats Maynott.