The Time dragon was originally a weapon created by Zorgo to steal the time energy from the Doctor's TARDIS, and with partial success. However the dragon began growing in size and spitting vortex energy - which one blast hit Zorgo. The Twelfth Doctor and Clara jumped on the dragon and flew away to plug the hole in time and then find his TARDIS. (COMIC: Zorgo the Terrible.
On the 26 September, 2016, the Doctor arrived using the time dragon as a substitute for his TARDIS. He picked up Gertie and Charlie and arrived outside of their house. Due to its connection with the TARDIS, it was able to regurgitate the TARDIS along with its time energy - and thus became a normal robot dragon. (COMIC: Super Gran).