Ah, yes. Bill Cipher. Our favorite interdimensional dream demon, very spicy dorito, human puppeteer (he's not human; the puppets are), drinker of human soda, (sorta), and future overlord of the multiverse. His hobbies include invading people's minds, possessing innocent twelve year-olds, causing catastrophic events, messing up people's faces, taunting humans whenever possible, kidnapping people, torturing people, and trying to kill children.
And now, unforgettable lines: "That sounds like a great offer. How 'bout instead I shuffle the functions of every hole in your face." "SORRY KID BUT YOU'RE MY PUPPET NOW!" "Ha, I'm insane either way brainiac." "I liberated my dimension, Stanford. And I'm here to liberate yours." "Name's Bill, but you can call me your lord and master for all of eternity!" "yOu TwO wAiT hErE; i'Ve GoT sOmE cHiLdReN i NeEd To MaKe InTo CoRpSeS." Ok, I think that's enough lines lol.