What is Horton Hears A Who about?

In Horton Hears a Who!, which is no doubt one of Dr. Seuss' most famous and widely-read books, Dr. Seuss tells the story of the eponymous Horton the elephant, who continually goes out of his way to save the people of Whoville from the evil animals which surrounds them. In fact, these animals want to incinerate Whoville, thereby killing all who live there. But Horton, who has a big heart and is gentle, can’t let that happen, so he works as hard as he can to stop the animals.