2nyRiggz said:Does the doctor always change face..how often or they just play it off like the new actor was always the doc?
In terms of plot, the doctor can "regenerate" his body when near death. He looks the same and acts slightly differently but he's still the same character with the same memories, abilities etc. The other characters and the doctor recognise that he has changed physical, though he is the same person.
There's no set point to when the regeneration happens, usually when the lead actor wants to leave or is forced to leave.