Lisa Marie Simpson is a fictional character in the animated television series The Simpsons. She is the middle child and most accomplished of the Simpson family. Voiced by Yeardley Smith, Lisa was born as a character in The Tracey Ullman Show short "Good Night" on April 19, 1987.
Vote which fictional character would naturally fit in-universe with a big-named franchise! No time-travel, no interdimensional crap, no "Pooh's Adventures", they would just exist in-universe.