Lisa Marie Simpson, voiced by Yeardley Smith, is Homer and Marge's oldest duaghter and the middle child on The Simpsons.  Lisa is very intelligent, plays the saxophone, is a vegetarian, Buddhist, and definitely a bit of a young political activist.  She's basically the complete opposite of her brother, Bart.

Lisa Simpson Quotes

Lisa's Brain: Poor predictable Bart. Always takes 'rock'.
Bart's Brain: Good ol' 'rock'. Nuthin' beats that!
Bart: Rock!
Lisa: Paper.
Bart: D'oh!

(at Aunt Gladys' funeral, Lisa goes up to the casket)
Lisa: Goodbye Great Aunt Gladys. I'm sorry I didn't get to know you better
Bart: (in a raspy voice from behind the casket) Don't worry about it
(Lisa runs away screaming; Bart laughs)

The Simpsons Quotes

Homer: (Wearing glasses) The sum of the square roots of any two sides of an isosceles triangle is equal to the square root of the remaining side!
Man: (From inside a bathroom stall.) That's a right triangle, you idiot!
Homer: D'oh!

Wow, now I see why they call you Miss Hoover. You must have been vacuuming for an hour.

Bart