The Doctor
The Doctor is the last of his race, the Timelords, which was destroyed in the Time War. He was born in Gallifrey and travels through time and space in his TARDIS, which looks like a blue police box. Originally the TARDIS (Time And Relative Dimensions in Space) was able to change its appearance to blend in to its surroundings, but that feature has been long broken, much like many of its functions.

The Doctor often travels with companions. His greatest rival is The Master. His enemies are the Daleks. 

He may sound like he's from the North, but in actuality, he's an alien, and lots of planets have a North for your information. 
"Who are you?"

"The Doctor."

Doctor who?"

"Just the Doctor."