Credit: Flickr Photo: Nickelodeon

It's a sad day for all of us who love the Nickelodeon golden oldies. Steve Viksten, who voiced the always hysterical Oskar Kokoshka on Hey Arnold! and wrote several of the episodes, passed away Monday at the age of 54. The cause of his death has yet to be determined.

Check out the Youtube video below for the best Oskar Kokoshka moment: "Pet the kitty."

Steve didn't only write for the television series, he also wrote the “Hey Arnold!” movie, as well as some fan-favorite episodes including “Arnold’s Hat” and “Stoop Kid.” Other shows in his writer's rolodex include episodes of “Rugrats,” “Recess,” “Duckman” and “The Simpsons.”

"We are deeply saddened to learn that Steve Viksten has passed away. Steve was a gifted artist and we were honored to have the opportunity to work with him on our beloved shows 'Hey Arnold!' and 'Rugrats.' Our heartfelt condolences go out to his loved ones," a Nickelodeon representative said in a statement to The Huffington Post.

We will miss you, Steve. Thanks for making our childhoods so much better!

What was your favorite Oskar moment from Hey Arnold!? Relive your favorite old school Nickelodeon moments in the comments below!

Source: The Huffington Post, The AV Club, Youtube