King Friday XIII is the imperious monarch of the Neighborhood of Make-Believe in Mister Rogers' Neighborhood. He is relatively egocentric, irrational, resistant to change, and temperamental, although open-minded enough to listen when told he is wrong. He has a fondness for giving long-winded speeches and using big words. Despite these qualities, he's basically a good regent, capable of summarizing the lesson he has learned after something has gone wrong.
He is also seen briefly hanging in Stewie's fantasy dream in "Brian in Love".