K-9

K-9
Aliases	K-9 K•9
Species	Robot
First Appearance	The Invisible Enemy
Last Regular Appearance	Warrior's Gate
Main Actor	John Leeson
Other Actor(s)	David Brierly

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, Sarah Jane Smith, The Eleventh Doctor, the Rogue, Will Adams and Kendra.

K-9 Mark I, II and III addressed whoever was directing them as “Master,” or Mistress” depending on the gender, and used the formal “affirmative” and ”negative,” rather than “yes” or “no”. They were programmed to be loyal and logical. With a penchant for taking orders literally, almost to a fault. Their striped collars mimicked the Fourth Doctor's trademark scarf.