Well, there are quite a few characters created by Dr. Seuss. But as far as I know, the character named King could be from 'The 500 Hats of Bartholomew Cubbins'. But it's not a definite answer.
Yes, some Dr. Seuss books can be considered novels. For example, 'The Cat in the Hat' has a narrative structure with characters and a plot that unfolds, which are characteristics of a novel, though in a very simplistic and child - friendly form.