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

Anya: (in a girls voice) "Dear Lisa, as write this, I am very sad. Our president has been overthrown...(man's voice) and replaced by the benevolent General Krull! All hail Krull, and his glorious new regime! Sincerely, little girl."
Lisa: (groans)

Homer: Do you really need all these Kurt Vonnegut novels?
Lisa: "They self-reference each other!"

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!

Labor Inspector: This plant violates every labor law in the book. We found a missing Brazilian soccer team working in your reactor core!
Mr. Burns: That plane crashed on my property!