K-9 (Doctor Who)

K9 occasionally written as K-9 or K•9 was the designation given to a series of intelligent, dog-like robots who served as companions of Professor Marius, the Fourth Doctor, Leela, Romana, the Mistress, Sarah Jane Smith, Luke Smith, Starkey, and the Tenth Doctor.

K9 Mark I, II, III, and IV addressed whoever was directing them as "Master" or "Mistress" depending upon gender, and used the formal "affirmative" and "negative" rather than "yes" and "no". They were programmed to be both loyal and logical, with a penchant for taking orders literally, almost to a fault. Their striped collars mirrored the Fourth Doctor's trademark scarf.