Devon is voiced by Eric Idle, who also voiced Slyly. Cornwall was voiced by the late Don Rickles, who also voiced Mr. Potato Head.
They are conjoined dragons, with Devon being a tall, thin, slim dragon whilst Cornwall is a short, fat dragon.
Devon and Cornwall hate each other so much that they even sing a comical song about not having each other ("If I Didn't Have You"). However, they cry upon hearing "Looking Through Your Eyes." Eventually, they are able to overcome their differences.
When flying their human friends, they even talk like airline pilots.
John Cleese and Rowan Atkinson were considered for the role of Devon and Dennis Miller and Steve Martin were considered for the role of Cornwall.