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: (To Erika) I'm not Drake.
Ross: That's right, he's not Drake. He's Hans Ramoray, Drake's evil twin.
Erika: Is this true?
Rachel: Yes, yes it is true. And I know this because, because he pretended to be Drake to, to sleep with me.
(Throws water in Joey's face)
Monica: And then he told me he would run away with me, and he didn't.
(Throws water in Joey's face)
Chandler: And you left the toilet seat up, you bastard!
(Throws water in Joey's face)

Friends Quotes

Chandler: Joey's tailor... took advantage of me.
Ross: What?
Joey: No way, I've been going to the guy for twelve years.
Chandler: Oh come on, he said he was going to do my inseem, then he ran his hand up my leg and then there was definite...
Ross: What? (Chandler closes his eyes)
Chandler: Cupping.
Joey: That's how they do pants! First they go up one side, they move it over, then they go up the other side then they move it back, and then they do the rear. Ross, will you tell him. Isn't that how a tailor measures pants?
Ross: Yes, yes it is... in prison!

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.