The Doctor is a Time Lord, an extraterrestrial from the planet Gallifrey, who travels in a time machine called the TARDIS.
Sometimes he is accompanied by companions who have chosen to travel with him for a variety of reasons.
Although he physically resembles a human, as a Time Lord his physiology is different. Once a Time Lord suffers a mortal injury, illness, or old age, he uses the ability to regenerate.
"I told you; The Doctor."
"Yeah, but, Doctor who?"
"Just The Doctor."
The Doctor. The Doctor is a Timelord from Gallifrey, which in the recent series has been revealed to be destroyed. He usually saves the Earth/The Universe/Civilisation as we know it on a day-to-day basis. Generally talks alot, though it varies from regeneration to regeneration. Often, no, almost always has a compainion (A friend - not that way either.) travelling with him. Want to know more? Wiki has a large article on it which can explain it better than i can. Just look up 'Doctor who'
2. The Doctor saved the universe again. Man, and I thought i was accoplished.
Whovian: 10nth used to say "Allons-y", which meant "Let's go" in French.
Mom: Forget about the Doctor Who stuff.
Whovian: NO, NOT LIKE DONNA NOBLE.
He's the most fantastically good man throughout all of time and space, and yet he gets so little.
At the end of the day, he's just an oft lonely man who travels around the universe in a little blue box. And that's what makes him so brilliant.
"I'm the Doctor."
"The Doctor? Doctor who?"
Friend: I know. It's all you talk about.
Whovian: Because... Doctor Who... SO GOOD.