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.: Sticks and stones may break my bones...
J.D.'s Narration: ...but words will hurt forever.

J.D.: Anyway, about this whole setting the date thing: I mean, I'm really psyched for you guys, it's just gonna be harder and harder for us to hang out, you know? I mean, you're gonna be married, man! You're gonna have, like, a house! You know? You're gonna be spending your weekends chasing around little Arturo and Rosaria!
Turk: You mean Tamika and Fuquan?
J.D.: You should... talk to Carla...

Scrubs Quotes

And bam!! The shines off the apple. And thats when you find out that that pretty little girl you married isn't a pretty little girl at all. No, she's a man eater. And I'm not talking about the "whoa here she comes" kind of man eater, I'm talking about the kind that uses your dignity as a dish towel to wipe up any shreds of manhood that might be stuck inside the sink. But of course, I may have tormented her from time to time, but honest to God that's what I thought marriage was all about, so much so that by the end of that relationship, I honestly don't know who I hated more...her or me. I used to sit around and wonder why our friends weren't trying to destroy each other like we were. And there it turns out the answer's pretty simple. They weren't unhappy, we were

Dr. Cox

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?