I refer you to the great article by Nadia Drake in the July 2015 issue of the National Geographic magazine entitled "Pluto at Last." In it Drake told the story that it was an 11-year-old girl from England who proposed, in 1930, the name Pluto after the Roman god of the underworld. Some people suggested that she got the name from Walt Disney's cartoon dog. However, although the dog did make his premier in 1930, he didn't acquire the name Pluto until 1931, a year after the girl proposed the name.
Be sure to watch the National Geographic Channel for Pluto Encounter on July 15 at 8 p.m. for a film about the mission.
Drake, N. (2015). Pluto at last. National Geographic, 228(1), 112-123.