Possible Clues:

• "A Boy Named Sue" writer Silverstein
• Writer/ illustrator Silverstein
• First name in children's literature
• 'Who Wants a Cheap Rhinoceros?' author Silverstein
• Silverstein of kid lit
• 'A Boy Named Sue' songwriter Silverstein
• “A Boy Named Sue” songwriter Silverstein
• 'Spaghetti' poet Silverstein
• Silverstein who wrote 'Once there was a tree, and she loved a little boy.'
• Fills