Harold Scrubb was the father of Eustace Scrubb, and Alberta Scrubb's husband. He was also the uncle of the Pevensie children. (It is unknown whether he was related to Helen Pevensie, or if he was related to the Pevensies through his wife instead.)
Harold and his wife were very progressive people. They were non-smokers, teetotalers (non-alcoholics), vegetarians, pacifists, and republicans. The couple also wore a special kind of underwear. They put very little furniture in their house and very few clothes on their beds, and the windows of their house were always left open.
In 1933, Alberta had a son, whom she and Harold named Eustace Clarence Scrubb, and called Eustace Clarence. They raised him to be as modern and progressive as they were, and taught him to call them 'Harold' and 'Alberta' instead of Mother and Father.
Alberta was proud of what some would call her son's snobbishness and fondness for making other people miserable, and although Harold's opinion is not recorded, it can be assumed that he was at least not disgusted by his son's character.
Relationship with Pevensies
Mr. Pevensie and Helen Pevensie arranged with Harold and Alberta for Lucy and Edmund to go stay at their home for a short time in 1942, while they and Susan were away on holiday, and Peter was studying for his exams. The Scrubbs were known to have visited the Pevensies at their house the previous year, and most likely the two families had visited each other many times before.
In the Voyage of the Dawn Treader film, Harold was a quiet man who spent his time listening to the radio or reading the newspaper, and was not very interested in spending time with his family, or at least with his niece and nephew. He literally ignored Edmund and Lucy when they returned home with the groceries, despite Lucy making repeated attempts to talk to him.