In Doctor Who, K-9 is a mobile computer in the shape of a dog. He was constructed by Professor Marinus to be a companion for him whilst working at a medical foundation in deep space. K-9 is a huge database and has defensive capabilities, being equipped with a retractable laser in his nose which can be set to stun or kill. He can integrate with virtually any computer system, including the TARDIS, and has also helped The Doctor escape many a tricky and dangerous situation. The Doctor rebuilt K-9 several times, upgrading and improving each version.