Because of the weight penalties, Professor Marius of the Center for Alien Biomorphology - the Bi-AI Foundation - was unable to bring his pet dog with him from Earth. Being somewhat sentimental, as well as eccentric, he built his data-analyzer computer into the form of a dog and called her - him - it 'K-9'.
K-9 has many canine characteristics - he is loyal, brave and obedient. He also has several human traits - curiosity, stubbornness and a rather benevolent air of complete superiority towards other creatures, great and small. Although he claims to be a machine and therefore without emotion, he displays common canine attitudes; for example when a 'friend' approaches - his tail wags. Professor Marius spent a great deal of time and effort to keep K-9 as companion-like as possible. The mechanical version of man's best friend has nuclear antennae for ears, computer printout for a tongue, a radio antenna for his tail and a blaster gun instead of teeth.
He is, as every 'K-9' should be, a loyal friend and formidable enemy. And sometimes quite infuriating.
BBC Character Outline.