Voyages of Doctor Dolittle, The by Hugh Lofting (1886 - 1947)

Doctor John Dolittle is the central character of a series of children's books by Hugh Lofting. He is a doctor who shuns human patients in favour of animals, with whom he can speak in their own languages. He later becomes a naturalist, using his abilities to speak with animals to better understand nature and the history of the world.(summary from Wikipedia)