Back in the day, Hey Arnold was the pinnacle of all Nickelodeon cartoons.

It had a diverse cast, a great soundtrack as well as tackling some pretty important issues.

Here are a few little facts that you might not have known about the ’90s classic.

1.

The show had some very dark hidden secrets. Just look at the design of Grandpa’s face – that can not be accidental.

2.

A lot of mature themes were explored within the show. For example it’s pretty safe to assume that Helga’s mom was an alcoholic. She would pass out, slur her speech and had her drivers license taken from her.

3.

All of the girl characters in the show were based on the show creator, Craig Bartlett’s, childhood crushes.

4.

Arnold’s city is based on a few different places including Seattle, Brooklyn and Portland. The name of the city is never revealed but fans have guessed that it’s called Hillwood as the pharmacy is called Hillwood City Pharmacy.

5.

The creator of the show, Craig Bartlett, is actually Matt Groening’s brother-in-law. If you don’t know, Matt Groening is the creator of The Simpsons.

6.

It was Barlett’s wife that came up with Helga’s crush on Arnold – a running theme throughout the show. Lisa Bartlett has since explained: “I just didn’t want to see another bully girl, like that mean one on Rugrats. Bullies have feelings, too, right?”

7.

While there were in fact hints to Mr Simmons being gay, Craig Bartlett has since confirmed it. One of the more obvious hints was during the Thanksgiving episode, where Helga and Arnold crash his family’s dinner and Mr Simmons’ “friend” Peter is there. Mr. Simmons’ mother says, “I didn’t know Peter was coming today” to which Peter responds, “There’s a lot of things you don’t know.”

8.

The idea for Hey Arnold began on Sesame Street as a Claymation.

9.

All of the children on the show were voiced by children. This was the first cartoon on Nickelodeon to do so.

10.

Michael Landon from Little House on the Prairie actually inspired one of the characters on Hey Arnold. Michael’s birth name was Eugene Orowitz, which obviously inspired the name Eugene Horowitz.

11.

There is no mentioned of it in the show, but Arnold does in fact have a last name. It turns out all of those times Grandpa called Arnold “shortman” was for a reason. During Comic Con, Craig Bartlett confirmed that Arnold’s full name was in fact “Arnold Shortman”.

12.

Arnold was actually voiced by six different across. The four that get the most credit are Toran Caudwell, Phillip Van Dyke, Spencer Klein, and Alex D. Linz