K-9 (voices of: John Leeson & David Brierley)
Professor Marius of the Bi-Al Foundation designed and built K9 to be, in effect, his protable computer and doglike companion. K9 is mobile, battery powered and capable of independent action and thought. He communicates with his master by speech; an extendable probe in the center of his forehead allows K9 to make contact with machines and other computers - including the TARDIS's - to exchange information.
Always logical and precise, K9 can be infuriating to work with as he will orally correct the errors of his master or mistress. His responses are short, confined to one word questions such as "Master?" or "Mistress?" or brief replies such as "Mission accomplished", "Affirmative" or "Negative", and delivered in a rising electronic voice. The accuracy of his English can be quite humorous, counterpointing the sometimes vague requests or statements of the Doctor.
K9 can reliably store and recall data using his computer circuits. He has been programmed with everything his inventor knows and can rapidly assimilate new information, even though he may not be able to explain it simply. For a robot, K9 has an inquiring mind. Highly sensitive scanning systems allow K9 to report on the presence of approaching people or creatures, including their numbers and probable intent.
The greatest weakness of K9 is his reliance on battery power: he needs recharging from time to time, especially when he is forced extensively to use his blaster. The Doctor also cannot resist tinkering to repair or improve parts of K9, leaving him out of action and in bits in the TARDIS.
K9 is ingot-shaped, about 50cm tall, 80cm long at the base and built out of a grey metallo-plastic. A push button control panel is located in the center of his flat back. K9's flat-sided, doglike head is attached to his body by a flexable, ribbed link, around which hangs a tartan dog collar. Two curved antennas on his head act as tracking and audio sensors; his tail is a radio aerial. His visual circuits are protected by a red panel running across his forehead. A raised cowling on his snout conceals a blaster that has to be extended for use. K9 can issue printed reports using the hard copy output located in his mouth.
The Doctor can summon K9 by blowing on a sonic whistle to which K9's audio-circuits are programmed to respond.