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

Rachel: Julie! Julie, isn't that great? I mean, isn't that just kick-you-in-the-crotch, spit-on-your-neck fantastic?
Monica: (To Julie) It's an expression.

Monica: Hey, Joey! What would you do if you were omnipotent?
Joey: Probably kill myself.
Monica: Excuse me?
Joey: Hey, if Little Joey's dead, I got no reason to live.
Ross: Uh Joey... omnipotent.
Joey: You are? I'm so sorry. (To Chandler) I didn't know, I thought it was one of those theoretical questions.

Friends Quotes

Rachel: Daddy! Daddy listen to me! It's like all my life everyone's told me, "You're a shoe! You're a shoe! You're a shoe!" Well, what if I don't want to be a shoe? What if I wanna be a purse or a hat? No I don't want you to buy me a hat, I'm saying I am a hat. It's a metaphor Daddy!
Ross: You can see where he'd have trouble.

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.