Because you like Porthos in The Three Musketeers
Catherine Linton was once spontaneous and rowdy but ever since marrying the wealthy Edgar, she has morphed into a boiling pot of emotional outbursts. See them in Wuthering Heights.
A dedicated hedonist, Jack Harkness appreciates raunchy stories, stiff drinks, and excellent bottoms. See them in Doctor Who.
Jasmine dreams of something more than palace life, and she's not afraid to go get it. See them in Aladdin.
Klaus Baudelaire's photographic memory saves the lives of his siblings many times over. See them in Lemony Snicket's A Series of Unfortunate Events.
Mother Gothel is a great mother as long as you never, ever, break the rules. See them in Tangled.
Morticia Addams hates anything bright and cheery and loves all things ghoulish, ghastly, and violent. See them in The Addams Family.
Vanellope von Schweetz is princess of the Sugar Rush game who could care less about being royal. See them in Wreck it Ralph.
Give in to the dark side with vampire Lestat; it's more fun. See them in Interview with the Vampire: The Vampire Chronicles.
There is never a dull moment with Jim Moriarty: expect booze and sing alongs in between all of the homicide. See them in Sherlock.
Egon Spengler prefers collecting spores, molds, and fungus to interacting with people. See them in Ghostbusters.
Point the fun-loving Pippin Took towards second breakfast, and he's one happy hobbit. See them in The Lord of the Rings.