K-9 was created by Professor Marius in the year 5000. 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.
Cyberman originally born on Earth's twin planet Mondas, the Cybermen were created as the Mondasians replaced parts of their dying bodies with plastic and steel. Eventually they added emotional inhibitors, suppressing all feelings - love, hate, even fear.
The Daleks are one of the most feared races in the universe. Their creator, Davros only has one intention, destroying all life apart from Dalek life. The Doctor has stopped them on several occasions but somehow they keep coming back!
TARDIS (Time And Relative Dimension In Space) is a product of the advanced technology of the Time Lords. A properly maintained and piloted TARDIS can transport its occupants to any point in time and space. The interior of a TARDIS is much larger than its exterior.