Dr.
Wayne Dyer, an author and motivational speaker. (Source: http://www.pixar.com/shorts/d&n/4.html)
The voice used in this film is from Dr. Wayne Dyer and was taken from a lecture he gave in the 1970s. The director of the film incorporated the ideas taken from Dyer's lecture in order to show that the unknown can be mysterious and beautiful, and doesn't at all have to be something to fear. Pixar honored Dyer by providing him with a private screening of the film.