From the Super Mario Wiki, the Mario encyclopedia
Not to be confused with Ottō.
“Ooh, MOMMA, did I get some interesting info from a buddy of mine! He swore to me to secrecy, look like you can keep quiet, so I'll tell you. And now, I blow your mind... Eat mushrooms to restore your HP! Got that? Did you hear me? That's some PRIME info, huh? Keep it under you hat!”
Otto, Super Paper Mario

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.