Floorboard Harry was a character cut from the episode "Graveyard Shift."
Harry‘s face has never been seen. Even when he (infrequently) leaves his home under the floor of the Krusty Krab he travels with a mobile section of floor to hide behind. The fact that he has fingers would suggest he is not a fish, but this has not been confirmed.
He would have played the role of the character that took his place, Nosferatu, who was responsible for turning on and off the lights. Additionally, a gag earlier on in the episode would feature SpongeBob delivering mail to him. The Nautical Nonsense and Sponge Buddies DVD features Tom Kenny and Rodger Bumpass recording said scenes.