Horton Hears a Who is a children's book written by Dr. Seuss in 1954. The story follows an elephant named Horton who discovers a tiny planet called Whoville, inhabited by microscopic creatures called Whos. The phrase 'Horton Hears a Who!' is used to refer to the moment when Horton discovers the Whos and their world. The crossword solution for this term is WHO, which is the name of the inhabitants of Whoville.