Harold has known Angelica and Susie since pre-school, and reminds them of that fact every chance he gets. He is good natured and means well, but Harold can tend to be a bit annoying, to say the least. His social skills have a lot to be desired, and he often matches Phil in terms of grossness, although most of the time he is oblivious as to how gross he is. Despite her constant put-downs, Harold dotes on Angelica, and he may be the only guy out there who worships her the way she wishes everyone would. - All Grown Up! Description from Klasky Csupo.
In the Rugrats series he is a bit overweight, but loses this trait in All Grown Up!. He normally wears a green shirt, a pair of dark blue shorts, and light blue sneakers. He has curly, Afro-like, orange hair as well. In the Rugrats spin-off Preschool Daze, he wears the same outfit as worn in the Rugrats series. In All Grown Up!, he wears a blue shirt with brown pants and green sneakers.
- Harold is Angelica's trustworthy assistant in the 2004 video game, "All Grown Up!: Express Yourself".
- Harold enjoys giving advice to people as shown in the All Grown Up! episode, "Bad Kimi", when he takes control of the "Ask Angelica" website when Angelica was busy. Once Angelica came back, he started up his advice chat log and provided assistance to his fellow peers, though he could not deal with the pressure and eventually gave up and went back to Angelica.
- According to Harold in "Saving Cynthia", Rodeo Man is his favorite superhero.
- According to Harold in "Rats Race", his mom is a mechanical engineer.
- It is revealed in "Rat Traps" that Harold is an excellent figure skater.
- Harold is successful at making Angelica jealous of him in "Ladies' Man (Ladies' Boy)".
- He likes to dress up as "Killer Bee Boy", as shown in "Super Hero Worship".
- His middle name is revealed in "Miss Nose it All" as Wayne.
- He likes gross stuff and wants to be a firefighter like his dad.
- He has a crush on Angelica.