“Hey Arnold!” is a popular animated television show that aired on Nickelodeon from 1996 to 2004. The show is set in the fictional city of Hillwood and centers on the life of a young boy named Arnold, who lives with his grandparents in a boarding house. Here’s a list of some main and notable characters from the show:

1. Arnold – The titular character, a kind-hearted and optimistic boy with a football-shaped head. He’s known for his iconic little blue hat and plaid shirt. He often acts as a problem solver and mediator for his friends and even some adults.
2. Helga Pataki – A girl who secretly has a crush on Arnold but outwardly bullies him. She often refers to him as “Football Head.” Helga is known for her unibrow and pink dress.
3. Gerald Johanssen – Arnold’s best friend, known for his tall hairdo. He’s loyal, smart, and often assists Arnold in his adventures.
4. Phoebe Heyerdahl – Helga’s best friend and the smartest kid in their class. She’s shy and supportive and often plays the voice of reason.
5. Grandpa Phil and Grandma Gertie – Arnold’s quirky grandparents who run the Sunset Arms boarding house where Arnold lives.
6. Stinky Peterson – A tall, skinny boy with a Southern accent who comes from a farming family.
7. Harold Berman – A bully with a soft side, he’s larger than most of his classmates and is often seen picking on others.
8. Sid – One of Arnold’s friends who’s a bit paranoid and superstitious but means well.
9. Lila Sawyer – A sweet and perfect girl that Arnold once had a crush on.
10. Eugene Horowitz – The class jinx who is clumsy and often has a streak of bad luck.
11. Mr. Simmons – The kids’ sensitive and understanding 4th-grade teacher.
12. Big Bob Pataki – Helga’s father who owns Big Bob’s Beepers, a beeper store. He often overlooks Helga in favor of her older sister Olga.
13. Brainy – A quiet boy who constantly sneaks up behind Helga, breathing heavily, often resulting in her punching him.
14. Rhonda Wellington Lloyd – A fashionable, rich girl in Arnold’s class who is obsessed with popularity.
15. Nadine – Rhonda’s best friend who’s interested in insects and is more down-to-earth.
16. Curly – A classmate with curly hair known for his unpredictable and sometimes crazy behavior.

This is by no means an exhaustive list. “Hey Arnold!” had a rich tapestry of characters, each contributing to the show’s vibrant depiction of urban life.