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

J.D.: Hey, I heard a great joke. A guy walks into a dentist's office and says, "I think I'm a moth." And the dentist says, "Well, if you think you're a moth, why are you at a dentist's office?"
J.D.'s narration: Oh, no, I forgot the punchline... You can't bail out now! Stall! Stall!
J.D.: ...So the moth says "That's a good question. What kind of dentist are you?" And the dentist says, "Well, I'm a general dentist, but I...I do dabble in orthodontry - braces and such." And... and the moth says, "Orthodontry? I hear there's great money in that."
J.D.'s narration: "The light was on"!
J.D.: "But! To answer your original question, which was, if I think I'm a moth, why am I in a dentist's office? The answer is, Because the light was on!" The light! The light, James. Moths love light. So, James, other than your funny bone being broken, what seems to be the problem?

Paige: You know what used to drive Perry nuts as a kid? Every night we'd play Horse in the driveway, and I'd always kick his ass.
J.D.: Can Christians say "ass" now? I have a friend - Pat Casey - he called his mom an ass once? She hit him in the face with an iron! He still goes to church, but he can't whistle anymore.