From the Super Mario Wiki
Otto is a resident of Flipside in the game, Super Paper Mario. He walks around on the first floor and is said to be very scatterbrained. Whenever one of the four heroes talks to him, he always gives them obvious info, saying it's a secret. However, he is honest and has common sense, so everyone loves him, especially the kids (according to Tippi). His Flopside counterpart is Ditto.