Sid is perhaps the most fashionable of the Hey Arnold! characters, besides Rhonda. His hero is Monkeyman, and he is usually seen with Harold and Stinky. He is generally known to be very superstitious, stubborn, and paranoid, having once believed to have killed his school principal with a voodoo doll carved from soap, and at another time believing that Stinky was a vampire. There was even a time where he was obsessed with being clean after learning about germs in his classroom, so much so that he wore a special anti-germ suit and could barely sit inside his desk while wearing it.
His most noticeable feature is his long nose, which seemingly protrudes from his forehead. He also has a pair of prized white Beatle boots, and a black jacket; he almost always wears this outfit. In the episode "Monkeyman", Sid was mugged by adolescent thieves who decided to steal his Beatle boots, although Monkeyman retrieved it at the end of the episode.