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!

Dr. Kelso: Now if any of you other would-be revelers get the urge to dress up on this, the mother of all non-holidays, please consider me the razor blade in your caramel apple. We're professionals, dammit! You know... it's nothing personal, son... you just make me sick.
Doug: He called me son! He called me son!
J.D.: Score.

Scrubs 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!

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?"