Monica Geller is a little bit crazy, but definitely seems to be the leader of the group of Friends.  She's Ross's sister and high school best friends with Rachel and kind of ties to the group together as a mother-like character.

Monica is known for being a little OCD and for being overweight in high school.  Now?  She's a bit of a chef but holds various jobs during the season.

At the end, Monica ends up marrying Chandler in season seven.

Monica Geller Quotes

Monica: What's "PLEH?"
Joey: That's help spelled backwards so that the helicopters can read it from the air!
Monica: Ah...what's doofus spelled backwards?

Joey: Some girl ate Monica!
Monica: Shut up, the camera adds ten pounds.
Chandler: Ah, so how many cameras are actually on you?

Friends Quotes

Phoebe: Okay, Joey, your bet.
Joey: I fold like a cheap hooker who got hit in the stomach by a fat guy with sores on his face. (The girls look at him, confused.) Oh, I'm out.

Monica: What's "PLEH?"
Joey: That's help spelled backwards so that the helicopters can read it from the air!
Monica: Ah...what's doofus spelled backwards?