From the Super Mario Wiki
Harold is a resident of Flopside in the game Super Paper Mario. His Flipside counterpart is a man named Walter. He is eighty years old and is married to a woman named Gertrude, having been married for sixty years (as told by his wife at the end of the game). According to his tattle, Harold is old-school, tending to keep his feelings to himself. After beating the game's story, talking to Gertrude results in her saying that, for the first time, Harold bought her a gift: the wedding ring he couldn't afford when they first got married. She states that he obtained it by working the graveyard shift at Notso's shop. Like Walter, he is only seen standing in place outside his house.
If spoken to during chapter 6, he will mistakenly refer to himself as "Walter".