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. [to Cox]: you won't admit this, but you're in love with Carla.
Carla: No, he's not.
Dr. Cox: Actually, I am.
Carla: You're starting again.
J.D.: And Carla, you're mad that Turk didn't trust you enough to tell you.
Turk: See? Trust, woman, trust!
J.D.: Whatever. The point is that Turk is sorry.
Turk: Not anymore!
Carla: I can't believe you thought he was a threat.
Dr. Cox: I'm a threat!
Carla: You're not in love with me, you idealize me.
J.D.: Can we just try and stay focused...
Turk: You're mad 'cause I'm scared of losing you?
Carla: Yes, because we're stronger than that!
Dr. Cox: Apparently not!

Lady: Love your Hairmet.
J.D.: Love yours!

Scrubs Quotes

J.D.'s Thoughts: Wait, is she in to me? Quick, make a bad joke and see if she laughs.
J.D.: Did you hear the one about the skeleton who couldn't go to the party? He had no body to go with.
Neena: That's really funny!
J.D.'s Narration: Well that's not a fair test - that joke's hilarious.

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?