Olivia Rose Olson (born May 21, 1992) is an American actress and singer-songwriter who voices Vanessa Doofenshmirtz on the Disney Channel animated series Phineas and Ferb. She is also best known for voicing Marceline in Adventure Time. She sings many of the songs in Phineas and Ferb, including a catchy duet called "Busted" with co-star Ashley Tisdale. She also sung "I'm Lindana and I Wanna Have Fun!", as Linda Flynn and "Ready for the Bettys" as The Bettys.