Cat

A cat was a type of predatory and usually small feline mammal. Cats came in a variety of colours and shapes and were commonly domesticated as pets. (PROSE: Human Nature)

The Tenth Doctor once claimed the cats on Earth weren't native to the planet, but were aliens. Rather than the prosaic names their human "owners" tended to give them, their actual names were much grander like "Great Hunter Grimalkin Greycoat Lionheart". Donna believed he was pulling her leg. (COMIC: Autopia)

Regardless of the truth of this claim, cats became extinct on Earth before the year 2157. (PROSE: Lucifer Rising)

Cats and the Doctor
The Doctor's relationship with cats varied.

First Doctor

 * A cat tried to attack the Doctor and his companions while they were shrunk to a small size. (TV: Planet of Giants)

Fourth Doctor

 * The Doctor used the story of Puss in Boots to befuddle a P-series Genesis III. He claimed the computer was unable to comprehend a talking cat. (PROSE: Inter-Galactic Cat)

Fifth Doctor

 * The Doctor found a cat while searching for a Kaled mutant on Earth. (TV: Resurrection of the Daleks)
 * Erimem brought a stray cat named Antranak onto the Doctor's TARDIS. (AUDIO: The Eye of the Scorpion) The Doctor disdained it. (AUDIO: No Place Like Home, Nekromanteia)

Sixth Doctor

 * This Doctor usually wore a coat with one of several cat brooches on its left lapel. (TV: The Twin Dilemma) The coat occasionally had a variable number of cat-shaped patches sewn into its lining. He sometimes touched his cat brooch for luck. (TV: Attack of the Cybermen) One of his cat badges seemed to change its expression to match the Doctor's mood. (WC: Real Time)
 * Whilst fighting off a transformation into an Androgum in 20th century Spain, the Doctor noticed a stray cat and was tempted to eat it. (TV: The Two Doctors)

Seventh Doctor

 * The Doctor was given a pet cat named Wolsey by Joan Redfern. (PROSE: Human Nature)

Eighth Doctor

 * The Doctor gave Wolsey to Bernice Summerfield. (PROSE: The Dying Days)
 * The Doctor enjoyed playing with and talking to Carolyn McConnell's pet cat Mina. (PROSE: Vampire Science)
 * The Doctor was given a tabby cat by Donna. (PROSE: Legacy of the Daleks)
 * When the Eighth Doctor was infected by Zagreus, among the avatars manifested by the Doctor's TARDIS to aid him was a Cheshire Cat straight out of Alice in Wonderland. (AUDIO: Zagreus)
 * The Doctor once met a cat who had been given the power of thought by the Bestiary of Legendary and Magical Creatures. (PROSE: Phoenix)

Ninth Doctor

 * The Doctor stroked the cat that stayed at the Imperial Club in London 1924. (PROSE: The Clockwise Man)
 * The Doctor picked up and began talking to a cat he found in 1941 London. (TV: The Empty Child)

Tenth Doctor

 * On encountering a cat, the Doctor declared he was not a cat person, given his recent experiences with the Sisters of Plenitude. Chloe Webber later drew the same cat, trapping it in a picture for the Isolus to play with. Along with the Doctor and all the other people and things in Chloe's drawings, it was restored by Rose Tyler. (TV: Fear Her)
 * Despite this, the Doctor seemed to have no qualms with petting the kitten offspring of Thomas and Valerie Brannigan. (TV: Gridlock)
 * The Doctor and Rose encountered a cat called Mitzi, a test subject which had been sent into Hyperspace and ended up ruling the planet Photris. After freeing the humans on Photris from Mitzi's control, the Doctor and Rose took Mitzi to the Powell Estate where she would be found and adopted by a younger Rose and Jackie Tyler. (DWS: The Cat Came Back)
 * The Hervoken used the Necris to force cats to attack the Doctor. (PROSE: Forever Autumn)

Eleventh Doctor

 * The materialisation of the TARDIS in 1890 France scared away a cat which had been resting in the alley. (TV: Vincent and the Doctor)
 * The Doctor conversed with a house cat to glean information about what was going on in 79B Aickman Road. (TV: The Lodger) Amy Pond stroked the same house cat. (TV: The Big Bang)
 * The Doctor mentioned "a basket of kittens" as one of the things people could think about to avoid experiencing fear which might attract the Minotaur. (TV: The God Complex)

Other cats

 * Frobisher took on a job to find a domestic cat of unknown variant. (AUDIO: The Maltese Penguin)
 * Jasper was a sapient cartoon cat, manifested from the mind of a young girl on the Crooked World. (PROSE: The Crooked World)
 * Amy Pond's favourite childhood cat was called "Biggles." (TV: The Girl Who Waited)
 * Estelle Cole owned a cat named Moses. (TV: Small Worlds)
 * Luke Smith and Clyde Langer once encountered an alien disguised as a kitten, which caused them to be late for school. (AUDIO: The Shadow People)

Behind the scenes

 * The non-canon video game Doctor Who and the Mines of Terror portrayed the Sixth Doctor travelling with a robot cat called Splinx.
 * An alternate Ninth Doctor once met a homeless cat lady. Upon noticing one dead, he said the cat "must have used up his nine lives, rather like me". (WC: Scream of the Shalka)