Brainy is a fictional character in the Hey Arnold! TV Series.
He is a very mysterious character often randomly showing up in places that are least expected whenever Helga G. Pataki is present, the most notable occasions being Haunted Train (in which, comically, he is the only character to witness the annual occurrence of the real haunted train).
He is voiced by series creator Craig Bartlett.
He is usually seen wearing a golden shirt with a white collar and brown pants underneath. He has spiky hair, wears round glasses and is constantly smiling eerily. By far, the most distinguishing traits of Brainy are his trademark wheezing and deep voice.
He is a quiet, kind of creepy kid who stalks Helga around. It is confirmed that he does know about Helga's crazy romantic obsession for Arnold.
- Brainy is the only one of Arnold's classmates not to be portrayed by a child actor.
- Brainy is one of the four characters who definitely knows of Helga's secret love for Arnold, the other three being: Dr. Bliss, Phoebe and Lila.