| Please note the following:
| ""Shut the fuck up! Your teacher will be here in a minute!"
— Steinbeck to Cody.
Principal Steinbeck is the cruel and somewhat insane principal of Bowser Junior's school. He loves it when the students get into trouble, so he can punish them. It is unknown why Principal Steinbeck is evil and how he became that way. He is very abusive and mean towards the students, but he appears to be nice and smooth-talking towards other adults, including the teachers. He made his debut as the main antagonist of Bowser Junior's Homework, which led him to be the main antagonist of Bowser Junior's Summer School.
In "Bowser Junior's First Grade Part 4" Principal Steinbeck has a conference meeting with the students and their parents. He says that they goofed up after enrolling Mr. Winkle as the new teacher. Bowser gets angry with him and asks why they didn't know he was a pedophile and thinks they didn't do enough background checks. Principal Steinbeck responds by saying that they tried everything, but has Officer Goodman explain the rest. As Goodman says that Mr. Winkle called him "hot" Principal Steinbeck remarks that he called him "hot" too and started to bicker angrily. After Joseph's Mom reveals they need more "Windex" Joseph remarks that that's not what was going on. Steinbeck laughs evilly and says that the next replacement teacher will be perfect.
In the Part 5 of the 1st Grade series, Bowser Junior answers the door to their apartment and sees Principal Steinbeck. He explains that he needs to see Bowser. So, Junior goes to Bowser's room and tells him that Steinbeck needed to see him. Then, Principal Steinbeck tells Bowser that they'll let Junior pass 1st grade and says that 2nd grade won't be easy.
He returns once more in First Day Of School, where Principal Steinbeck barges into the classroom and tells the students that if they fail, he'll punish them in the worst way possible. Cody asks when the teacher would arrive, but Steinbeck tells him to shut up. Afterwards, he leaves the classroom.
Likes and Dislikes
- Disrespectful students
- Pedophiles (specifically David Winkle)
- When a student passes (especially Junior)
- Bowser Junior
- He wore a hat in Bowser Junior's 1st Grade! Part 4. He also wore a different suit in First Day Of School!
- According to some fans, he is similar to The Joker from Batman.
- He is somewhat similar to Mr. Krupp from the Captain Underpants book series.
- Because he is a mean principal, Steinbeck is a lot similar to Principal Greedyguts from the Canadian animated series Jacob Two Two.
- In his first two appearances, he has a slight British accent, but in later videos, his accent sounds more American.
- Despite his insane and abusive disposition, Steinbeck is not completely evil, as he shows an intense dislike for pedophiles, because in Bowser Junior's Summer School 7, he calls the police when Bowser Junior told him he was being molested by Chef Pee Pee in the men's bathroom.
- He is believed by fans to be Charleyyy in disguise. This makes sense because of his ability to get along with Bowser so easily.
- It is revealed in Bowser Junior's 1st Grade! Part 5 that he liked to eat Doofy O's as a kid.
- It is hinted, yet unconfirmed that he is Joseph's dad, because in Bowser Junior's 1st Grade! Part 1, Joseph says that his mother sleeps with him.