Pook is an infant Adipose. Found aboard the TARDIS wandering alone by Alyssa, Pook was adopted as a pet. Neither the Doctor, nor Alyssa know where Pook came from or how he got aboard the TARDIS. Pook was later named "Pook" because of his repeated use of the word, the only word he is capable of verbalizing. The Doctor is unable to identify what "pook" means and the TARDIS is incapable of translating it. According to the Doctor, "pook" is not a word in the Adipose language.
Following the events that took place on the planet Gaia with the Doctor, Alyssa, Clara and Rusty the "good" Dalek, Alyssa discovered Pook wandering in a hallway in the TARDIS. Alyssa gave chase as Pook fled into a room and eventually found him hiding under a desk.