Doctor Jonathan Micheael "J.D." Dorian is the main character and narrator of Scrubs and is played by Zach Braff.  J.D. is best friends with Turk, who he's been friends with since they were roommates in college.  J.D. quickly meets Elliot, who he falls for hard and has an on and off again relationship with throughout the series. 

J.D.'s mentor is Dr. Cox who he is constantly trying to impress without making much headway.  He also has a bitter rival at Sacred Heart who torments him endlessly... The Janitor.  J.D. frequently daydreams where he tilts his head to the side and drifts away.

J.D. Quotes

And then the ultimate Cox-block.

J.D.

Dr. Cox: If you don't toss that shot back I'm gonna throw you on the counter and make you sing the theme song from 'Endless Love'.
J.D.: Yucky.
Dr. Cox: Yucky?
J.D.: Yucky.
Dr. Cox: Oh my God, I'm drinking with a Mousketeer

Scrubs Quotes

J.D.: My man Turk, is getting it daily and nightly and ever so rightly! Ah! What up, dogg!
J.D.'s narration: Once every 4.2 seconds a man says something stupid that a woman hears and punishes him for... luckily, this wasn't one of those times.
Carla: What did you just say?
J.D.: "What up...dogg?"

Sean: J.D., may I offer a little constructive criticism?
J.D.'s Narration: Kick him in the crotch dammit! The crotch!