His wife didn't like the name Mortimer Mouse she said it sounded "pompous"and that she preferred Mickey Mouse.
When Mickey Mouse spoke for the first time in 1929's The Carnival Kid his first words were Hot Dog,Hot Dog.
Walt was upset with how Mickey Mouse's voice sounded and lend his own voice to Mickey Mouse until 1947's Mickey And The Beanstalk when he said he was too busy to continue doing so.