K9 (Rose)

One K9 unit belonged to a possible incarnation of the Doctor that required the use of a wheelchair.

At a point prior to 5 March 2005, someone photographed the Doctor and K9. This photo would later be in the possession of Clive Finch. (PROSE:Rose)

Behind the scenes
Although it is not explicitly stated, the robot dog mentioned in the novelisation of Rose is intended to be a K9 unit.