Seeing as Ben and Sophie have put up favorite authors of their childhood, I though I would follow suit.
Steven Kellogg might not be the best children's author and illustrator, but he was my particular favorite when I was little. It was a staple of our library runs that I would head directly for his books in the children's section and see if they had any new ones. If they didn't, no great matter: I willingly read the old favorites over and over again. His stories about the Great Dane Pinkerton are the reason I still want a huge dog today. He wrote stories on everything from big dogs, to sea monsters, to imaginary islands, to American folk heroes.
His illustrations are fabulous, and so intricately detailed that you can stare at them for hours and still find new details.
I particularly like the weird stories he makes up...such as a boy who gets a tadpole that turns into a monster that he has to keep in a swimming pool and feed cheeseburgers...it's pretty awesome.