Harold is first introduced when he gets kicked out of the nursing home after seven years for stealing pudding cups and causing problems. Mario then picks him up and takes him back to his house. He usually forgets Mario's name and can't seem to agree on one thing to call him. He seems to be into opera music and doesn't like Mario's taste of modern rap music that much. He also expected Mario to become a doctor rather than a plumbing mascot for Nintendo. At the end of Mario's Grandpa, Mario calls another nursing home for an interview. He has shown signs of sexism and racism.
This version of Harold Puppet is from Melissa & Doug
In Super Bowl Commercials, Mario's grandpa is seen as the man trying out the Life Uhlert, where he is referred to as Harold. In Bowser Junior's 1st Grade!, Mario's grandpa is the teacher and introduces himself as Mr. Wilfred. This makes his complete name Harold Wilfred.
However this also means that Mario's name is Mario Wilfred apples to Nintendo's Mario "Jumpman" Mario. However, there is a possibility Harold Wilfred is Mario's maternal grandfather, which could explain why they don't have the same last name.
He still believes that the nazis are still around.