Our beloved hero has always been known only as 'The Doctor'. His name has never been stated in any form of media, and until recently it was used as a running gag in the show, when a character would respond by asking, "Doctor Who?". However, he chooses not to reveal his true name as it's something that can cause massive problems with the universe if spoken aloud (somehow). One particular point with his name regards the Time Lords, who, while stuck in a parellel universe, were trying to get him to state his true name so they would know which universe to come back to. Instead of divulging the name, Clara told the Time Lords that the only name that should matter is "The Doctor", as he has helped them and the universe numerous times under this guise. Lesson Learned: Who you are is nowhere near as important as what you do.