He is a fourth-grader who attends P.S. 118. He is in Arnold's class. Curly is most well known for his outlandish and bizarre behavior and freaking out to silly and trivial things (possible symptoms of psychosis, bipolar disorder, or borderline personality disorder). He is known as the "fourth-grader most likely to snap". He is considered one of the geeks ("Rhonda's Glasses").
Curly, ironically, has a "Moe" undercut hairstyle. He wears glasses, and his eyes are never seen until the episode "Curly's Girl" and again in "April Fool's Day." He wears a shirt with an orange collar, green for the upper half of his shirt and orange on the bottom half. He wears brown shorts and black shoes. In the episode "April Fool's Day", he wears a dark blue bowtie to the April Fools Day Dance with his regular clothes when he’s dancing the Tango with Rhonda Wellington Lloyd.
In Hey Arnold! The Jungle Movie, Curly is one of a handful of characters not to get a wardrobe overhaul. However, the shaved spot on the back of his head is more visible, and he now has small red Converse Sneakers with white socks.
Curly is one of the more prominent side characters, being subject to a few episodes. Curly comes across as a psychopath and will stop at nothing to get his revenge when he feels he has been wronged. He once framed Eugene for pulling the fire alarm with an elaborate plan just because Eugene sharpened his pencil down to the eraser ("False Alarm"). Though he has many psychopathic and/or sociopathic tendencies, Curly more than likely is not a psychopath or sociopath; Some fans believe that he has bipolar disorder.
Curly's most well-known act occurred in the episode "Curly Snaps." Because of a mistake in Mr. Simmons' plans, Sid became a ball monitor when Curly was supposed to. Because of this, Curly stole all of the school's kickballs and locked himself in Principal Wartz's office. He continuously made demands for soda and threw balls at students and staff from the window on top of the door. It wasn't until Arnold was able to calm him down, that the problem could be solved peacefully. Curly was then rightfully promised his ball monitor position for the week but was sent to detention by Principal Wartz.
In the episode "Ghost Bride," Curly is so outraged that he wasn't allowed to tell the story of the ghost bride because Gerald Johanssen is the keeper of the tales that he dressed up in a wedding gown and came to the cemetery in an attempt to frighten the kids to get revenge on them. On at least three occasions ("Ransom", "New Bully on the Block" and "April Fool's Day"), Curly can be seen dancing ballet, having taken dance lessons at Madame Bovary's ballet school for boys. It shows that Curly is a good dancer he even danced the Tango with Rhonda at the April Fools Day Dance. It is unclear whether or not Curly is an animal rights activist, or if he just decided to do something crazy when he freed the animals from the zoo in "Cool Party" (since in the same episode it's also said he bit the head of a chicken).
Curly is shown with his mother and father in "Parents Day".
Curly has a crush on Rhonda. In "Curly's Girl", he blackmails Rhonda into being his girlfriend for a week by telling her he can clean her mother's mink coat after Rhonda managed to make a mess of the coat with a candied apple. In the episode "Deconstructing Arnold", Helga gives Rhonda advice to confess her love to him in order to get Curly off of her back. The plan backfires as Curly humorously grabs Rhonda and kisses her saying, "Give Daddy some sugar."
Curly is one of the characters in the Hey Arnold TV series to be played by different voice actors.
- Steven Hartman ("Downtown as Fruits")
- Haley Joel Osment ("Deconstructing Arnold")
- Michael Welch ("Ghost Bride" and "Curly's Girl")
- Adam Wylie (all other speaking roles)
- Nicolas Cantu (Hey Arnold! The Jungle Movie)
Adam Wylie was Curly's main voice actor, but for some unknown reason, he was replaced and reinstated twice.
- Curly was inspired by a friend of Craig Bartlett in elementary school named Tim Jenson who once jumped onto his desk and sang the entire theme song to Daniel Boone.
- His favorite candy is licorice whips.
- He can be regarded as the male equivalent of Helga as they both have a similar head and nose shape, and antagonistic behavior and a crush on a certain person (with Helga's crush being Arnold and Curly's being Rhonda).
- Out of all the recurring child characters, he's the only one of two (the other being Alex D. Linz as Arnold) to be voiced by a child celebrity (Haley Joel Osment).
- In the episode "Cool Party", it is revealed that Curly's dad gives him bowl haircuts.
- He wears red socks.