A witches' cat serves no practical purpose whatsoever - they are to sit on the back of a witch's broomstick, and continue tradition. However, there is no actual rule stating that the witch's animals have to be cats, and theoretically even elephants could be permitted if it weren't for the obvious size restrictions. Owls, dogs, and even hedgehogs have been mentioned as alternative familiars. However, sometimes, certain witching schools will only allow a certain species to be the students' familiars (for example, in the 2017 series, Cackle's Academy only allowed cats.)
In The Owl and the Pussycat, we learn that familiars can lose their magic and will fade away if it is not restored. this can apparently happen when their owners’ magic becomes corrupt, but it turns out that when mother cats have kittens, they transfer their magic to the kittens, leaving the mother low on magic.
The first cat to be a witch's familiar was Ember. In the past, witches used any animal as a familiar. This changed when Victoria Cobwebton misjudged a flying spell and crashed in a village of non-magical people. The suspicious villagers threw Victoria in the village jail. Her familiar, a rabbit, was so frightened he ran away. Ember the cat squeezed through the bars to sit with Victoria, and she was able to remember the transference spell and used it to get herself and Ember out of the prison. She took Ember to the Witching Institute of Familars and they examined her and discovered that cats have an innate magical knowledge. From then on, cats became the most popular familiars for witches all over the world.
Tabby is Mildred's cat through her years at Cackle's Academy and Weirdsister College. Every witch was originally intended to have a black cat each, but since Miss Hardbroom found it unlikely that Mildred would ever pass the test, she didn't get a cat for her. Fortunately, she succeeded and the school granted her a gray and stripy cat which she named Tabby.
In the 2017 TV series, there wasn't a black cat for Mildred because she wasn't originally enrolled at Cackle's, but was only accepted on Selection Day.
He got his name because Mildred was surprised that he was the only tabby cat, so she exclaimed, "Tabby?!". He also rides in Mildred's backpack because he is afraid to ride on the edge of the broomstick.
Star is Mildred's dog, who she finds in her fourth year at Cackle's, after wishing for him on a shooting star. Mildred trains Star on her broomstick, where he displays a knack for doing tricks on the broom, as even cats tend to stay on the brooms and nothing more. After Mildred and Star are forced to perform in a multi-school talent competition, a group of elder witches note that there is no actual rule stating that the witch's animals have to be cats, and theoretically even elephants could be permitted if it weren't for the obvious size restrictions. Star becomes Mildred's broomstick companion after his tricks win the talent competition for Cackle's, while Tabby remains her general companion.
Midnight is Maud's cat, mentioned in the First Worst Witch book. The name was chosen, appropriately, at midnight, when Maud and her best freind Mildred Hubble were chatting about getting their kittens the next day. Midnight is not that good at flying, though she is better at it than Tabby. In fact, she started in about the same place as Tabby stayed at throughout the series. Like most cats, she is put to shame by Ethel Hallow's cat Nightstar. Midnight is described as a normal, easygoing black cat.
In the 2017 series, Maud briefly worried that Midnight was losing her magic, but it later turned out that she was just having kittens.
Stormy is Enid's cat, mentioned by name in The Worst Witch to the Rescue but renamed Teaser in the 1998 television series. Enid was training her to jump from the top of the wall onto her broom as it passed below at speed. Fortunately, Stormy was rather bold, unlike most cats, and wasn't bothered by sudden movement. Stormy really enjoyed this manoeuvre and was happily jumping from the wall, landing perfectly on the broom, zooming around the yard, and leaping back on the wall, supervised by a proud Enid.
In The Worst Witch Strikes Again (book), Monkey Business (TV 1998) and New Girl (TV 2017), Enid temporarily turned her cat into a monkey (named Muddles in the 2017 series, and Coco in the 1998 series).
Nightstar is Ethel's cat, mentioned in the First Worst Witch book. Like most of the other cats, he is black all over. Nightstar is very good at flying. He sits on Ethel's broomstick as if he is a model glued down. He is so good that he puts all the other cats to shame. Even when not on the broom, Nightstar sits bolt upright and still like a statue. Nightstar is very protective and territorial of Ethel and her broomstick. When Mildred's cat Tabby ended up on Ethel's broomstick, he kept on swiping down on his guest.
Ethel claims that Nightstar is a descendant of Ember, the first cat to be a witch's familiar.
Morgana is Miss Hardbroom's cat. Morgana was mentioned in The Worst Witch All At Sea. She is also mentioned (though not by name) in The Worst Witch Strikes Again, when Mildred accidentally pole vaults through HB's window and when Miss Cackle starts to tell her off, she is also 'removing a jam tart from her shoulder and absent mindedly feeding it to Miss Hardbroom's cat.'
Morgana is described as a particularly beautiful, sleek black cat with olive-green eyes.
Pendle is Miss Cackle's Cat, mentioned by name in The Great Wizard's Visit when he helps Maud find Miss Cackle when Agatha has enchanted her. Pendle Hill is a place in England that is associated with witch trials.
Ebony is Fenella Feverfew's cat. Ebony belongs to Harriet Goodcharm in the TV series. In The Worst Witch All at Sea, Miss Cackle suggests to Mildred that she replaces Tabby. A third-year witch, Fenella/Harriet, transferred to Miss Pentangle's Academy several mountaintops away and left behind her sleek black cat, Ebony, since they have owls at Miss Pentangle's instead of cats.
Ebony is almost as good as Ethel's Nightstar.
Lightning is Mrs Tapioca's cat, not really a witches cat, though she is Tabby's mother. Mrs Tapioca says that Lightning is "named right- "fast as lighting to take tinned food from bowl, but not mice!"
Kitty is a dog rather than a cat, but is Hettie Hubble's pet in The New Worst Witch. In episode 2, The Confidence Trick, the girls have to pass their broomstick flying test in order to stay at Cackle's. If they fail then they will be expelled. When the student witches pass, they are given a cat. When Hettie wishes she'd rather have a dog, Belladonna makes her wish come true by turning the dog her grandmother sent her into a cat in order to get her in trouble when it changes back. Miss Cackle then lets Hettie keep the dog, to the disappointment of Belladonna, whom Hettie names Kitty.
- Pocus is Felicity Foxglove's cat
- Sparkle is Sybil Hallow's cat
- Hazel is Clarice Twig's cat
- Solstice is Beatrice Bunch's cat
- Arcana is Miss Drill's cat
- Shadow is Azura Moon's cat