He arrived on Gallifrey in the Doctor's TARDIS and claimed to be the Doctor, having all of his memories. He was sent with the Twelve on a mission to find the Eighth Doctor and Bliss and investigate the Daleks' operations on the Ogron homeworld.
Bliss called him "Doctor Ogron" to not confuse him with the Doctor. They found a younger Doctor Ogron first being created by the Overseer, and the Doctor sent him to Gallifrey in his TARDIS to maintain the timeline. The older Doctor Ogron was exterminated by the Daleks but was restored to life by regenerating (though didn't fully change) after the Doctor, Bliss, the Twelve and the Daleks had gone. (AUDIO: Planet of the Ogrons)