Arnold - The central protagonist of Hey Arnold, Arnold is a dreamer and an idealist who always tries to see the best in people and to do the right thing. Whenever he sees someone in trouble, Arnold goes out of his way to help them out, whether or not it is sensible to do so. Arnold often acts as the stable center to those around him, whether he is around his 'family' in his grandparents' boarding house or around his friends at P.S. 118.

Helga - While Helga tries to maintain a tough exterior, in reality she is a sensitive, romantic girl. Helga has a difficult family life and is neglected by her parents, who would rather dote on her apparently perfect sister Olga than try to understand her. Because of this, she is insecure about herself; it is this insecurity which has made her into a bully. Helga also has had a crush on Arnold since the day they first met in preschool. While she feels that she must keep her crush secret, she expresses her true feelings through her various Arnold shrines and the poetry in her pink book.