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?

Ross: I hope Ben has a little sister.
Monica: Yeah. I hope she can kick his ass.

Friends Quotes

Chandler: Stick a fork in me, I'm done.
Phoebe: Stick a fork what?
Chandler: You know, like when you're cooking a steak.
Phoebe: Oh, I don't eat meat.
Chandler: Well how do you tell when vegetables are done?
Phoebe: Well you just, you know, you eat them and you can tell.
Chandler: Okay, then eat me, I'm done.

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?