Plagg is a kwami that is connected to the Cat Miraculous, and with his power, its wearer can use the ring to transform into a black cat-themed superhero, the current wearer being Adrien Agreste. He is one of the two deuteragonists (alongside Tikki).
Plagg is a small black creature that is 10 centimeters tall. He has a large head and small body. His appearance is very cat-like, having cat ears, a tail, two cat incisors, and green cat-like eyes, along with one whisker on his forehead and one whisker on each cheek.
At his best, Plagg can be described as being carefree and easygoing. At his worst, he is negligent, overindulgent, lazy, and sour. He isn't very helpful and doesn't take situations as seriously as he should. Quite the picky eater, he only enjoys eating cheese, particularly Camembert, which Adrien will feed him not only in order to fuel his transformation into Cat Noir, but also to bribe him when he's being uncooperative. He seems to like anything that is shiny and will also get distracted by anything that resembles Camembert, including Chloé's bracelet. Often making bad choices, like playing with Chloé's bracelet and causing an argument of it being stolen in the class after it gets stuck on his head, Plagg can be quite troublesome. He also seems to find others' misfortune amusing, especially Adrien's, along with dirty secrets they keep. However, Plagg does have a kinder side that comes out, and he will be serious if the situation requires him to be.
He tries to stop Adrien from transforming, as he hasn't finished explaining everything about the Cat Miraculous, in "Ladybug & Cat Noir", and he thinks Adrien's idea to talk Volpina out of causing harm isn't as useful as being Cat Noir in the episode of the same name.
Plagg is able to fly and levitate. Despite being small, he can carry objects larger or heavier than him, including a large slice of Camembert or a remote control. Also, he can phase through solid objects, like in "Volpina" when he phases through Gabriel Agreste's safe to get inside and unlock it for Adrien.
As a kwami, Plagg gives the wearer the power of destruction (bad luck) and transforms them into a black cat-themed superhero with the Cat Miraculous. Plagg, during the time his wearer is transformed, is aware of what is going on, albeit not able to communicate with them. For example, in "Dark Cupid", he remembers the events going on while Adrien was under the influence of Dark Cupid's arrow and lets him know he said a lot of bad things to Ladybug. Whenever the wearer uses Cataclysm, Plagg begins losing power and eventually can't retain the transformation any longer, leaving the ring and reverting the wearer back to normal. To be able to transform them again, he must refuel by eating, his choice of food being Camembert.
Thousands of years prior to the series, Plagg and the other Kwamis traveled the universe, unable to interact with any creatures, particularly humans. This was until a mage forged the Miraculouses, so Plagg and the others could both interact with mankind and grant them the ability to transform into heroes; Plagg and the Cat Miraculous able to give a person the ability to grant other people superpowers.
- Plagg's name is based on the word "plague."
- Plagg is based on a black cat, which, in some cultures, are symbols of bad luck.
- He is the kwami of destruction.
- He knows about Ladybug's secret identity.
- In Style Queen, it is revealed about Plagg:
- This is shown when Plagg was able to perform Cat Noir's Cataclysm by coming into direct contact with the tower's floor and thus destroying the entire structure.
- Plagg is responsible for multiple disastrous events in the past when he used his powers without his owners, such as making the dinosaurs and Atlantis disappear.
- He symbolizes the Yang.
- He is over 65 million years old.
- Plagg mentioned having a Miraculous owner for 5000 years it's revealed that Cat Noir's legacy is over 5000 years old.