Cats has such a vague plot that most of what fans believe is fanon.
- Jellicle cats have two forms: they're usually normal cats, but once a year they become Funny Animals.
- Victoria is an older kitten who is coming of age. In the plot, she's experiencing her first heat.
- Grizabella is shunned either because she's a sex worker or she worked for Macavity. The latter is Ascended Fanon in the 2019 adaptation.
- Many fans interpret Victoria as deaf. She's an all-white cat and all-white cats are frequently deaf (especially if they have blue eyes). Victoria also has no lines.
- Rum Tum Tugger is bisexual.
- Mr. Mistoffelees is gay.
- Before it was confirmed, Old Deuteronimy was believed to be Rum Tum Tugger's father; he's also canonically Munkustrap's father. Fan speculation is that he fathered Macavity.
- Bustopher Jones is either Mistoffelees' father or uncle.
- Rum Tum Tugger was temporarily turned into a hip-hop inspired "street cat". Fan Wank is that he's actually Rum Tum Tugger's son.
- Mungojerrie and Rumpleteazer are Half-Identical Twins. This has been confirmed in at least one production.
- Bombalurina is Grizabella's daughter and Munkustrap is Grizabella's son.
- Victoria's age is unclear but fans largely interpret her as the cat equivalent of 16-18.
- Mistoffelees, Victoria, Mungojerrie, and Rumpleteazer are around the same age.
- Mr Mistoffelees and Quaxo are the same cat. Either "Quaxo" is a nickname or "Mr Mistoffelees" is a Stage Name.
- Jellylorum is in a relationship with Gus, or else she's his daughter, with her playing Griddlebone to his Growltiger as Incestuous Casting.
- Demeter has previously been raped and/or kidnapped and held hostage by Macavity, or she was in a Masochism Tango relationship with him.
- Due to just how rare male calicos are, fans speculate that Mungojerrie is a trans man.
- Mr. Mistoffelees and Rum Tum Tugger are romantically involved.
- Though few of the familial relationships between the cats have been confirmed, some interpretations (mostly inspired by the 1998 version as well as common costume/makeup designs) have become so popular that a lot of fans now practically take them as read:
- Munkustrap, Macavity and Rum Tum Tugger are brothers and all were fathered by Old Deuteronomy;
- Alonzo is Tumblebrutus' father (and is also possibly Munkustrap's half-brother);
- Bombalurina and Demeter are sisters;
- Mungojerrie and Rumpleteazer are Skimbleshanks' children;
- Pouncival/Carbucketty is Jennyanydots' son;
- Victoria and Etcetera are sisters;
- Jemima is either Coricopat and Tantomile's daughter or younger sister (depending on whether you interpret the two as siblings or mates);
- Asparagus is Gus' son and Jellylorum is his daughter;
- Old Deuteronomy and Bustopher Jones (and possibly Gus) are brothers;
- Quaxo/Mistoffelees is Bustopher Jones' son
