K9 first appeared in the 1977 Doctor Who story The Invisible Enemy. K9 was created by Professor Marius in the year 5000. The Professor was a scientist working for the Bi-Al Foundation in the Centre for Alien Biomorphology on the asteroid K4067. The Doctor and his companion Leela helped Professor Marius defeat an alien virus. After the virus was defeated the professor asked if the Doctor to keep K9 and look after him.
After many adventures with the Doctor, K9 Mark I stayed behind on Gallifrey to look after Leela.
The original K9 Mark I first appeared in The invisible Enemy which aired in 1977, He last appeared in The K9 Series, Regeneration which first aired in 2009
K9 Mark I appeared in: The Invisible Enemy, Image of the Fendahl, The Sun Makers, Underworld, The Invasion of Time and K9 Regeneration
After the Doctor had said goodbye to Leela and K9 he entered the Tardis and brought out a large box with K9 Mark II written on it. Inside was a brand new K9 model.
K9 Mark II was the first model that the Doctor built himself.
Eventually K9 Mark II stayed behind in E-space with Romana.
K9 Mark II first appeared in The Ribos Operation which aired in 1979, He last appeared in Warriors Gate which aired in 1981
K9 Mark II appeared in: The Ribos Operation, The Pirate Planet, The Stones of Blood, The Androids of Tara, The Power of Kroll, The Armageddon Factor, Destiny of the Daleks, City of Death, The Creature from the Pit, Nightmare of Eden, The Horns of Nimon, Shada, The Leisure Hive, Meglos, Full Circle, State of Decay and Warriors Gate
In the 1981 TV story K9 and Company Sarah Jane Smith went to visit her Aunt Lavinia. Unfortunately Sarah Jane just missed her Aunt leaving for a lecture tour in America.
Inside the lounge was a large crate Sarah Jane’s Aunt had brought round, inside was K9 Mark III that the Doctor had left for her in 1978.
“Give Sarah Jane Smith my fondest love, Tell her I will remember her always” was the message left with K9 from the Doctor.
K9 Mark III first appeared in K9 and Company, A Girl’s Best Friend which aired in 1981, He last appeared in School Reunion which aired in 2006
K9 Mark III appeared in: K9 and Company, A Girl’s Best Friend, The Five Doctors and School Reunion
K9 Mark III got destroyed after defeating the Krillitanes so the Doctor built Sarah Jane a new one.
K9 Mark IV is currently helping Sarah Jane, Luke, Clyde and Maria in the Sarah Jane Adventures.
K9 Mark IV first appeared in School Reunion which aired in 2006
K9 Mark IV appeared in: School Reunion, The Sarah Jane Adventures and Journeys End
In the year 2059 Professor Gryffen was conducting experiments with an alien Space Time Manipulator. The original K9 got pulled through with some other aliens. K9 was forced to self destruct saving London from the aliens. With help from Starkey K9 was able to regenerate. After K9 regenerated he had no memory of where he came from, now he helps Jorjie, Darius, Starkey and professor Gryffen protect London from alien threats.