He made his first debut in The Bone Identity, when he introduced Avery as her nemesis. He is extremely rude, nosy and determined to find out what Stan's secret was. He's very good in math, while he entered the X-Square Game against Tyler and was disqualified for bad sportsmanship trying to bust Tyler for cheating.
Karl later returns in Dog Loses Girl, wanting to go to the water park with the family. The family is missing Chloe, and he happens to find her so he brings her back. Ellen then says he can tag along.
In Crimes of the Art, Karl is frustrated when his entry to the art competition is not chosen as the winner, and has a huge meltdown in front of everyone.
In Avery's Wild Party, Karl brings his sleeping bag to Ellen for her camping trip. After throwing their party, Tyler and Avery lie to her that they were throwing a party for Karl, so they convince him to act like it is his birthday.
In Don't Karl Us, We'll Karl You, Karl went under the alias of Walter Perkins, sending flowers to his neighbor Ellen. But Stan, Tyler, Avery, and Chloe come up with a plan to thwart his ways of visiting their house for good, and to stop his snooping presence towards Avery and Tyler especially.
In Avery-body Dance Now, Karl reluctantly teaches Avery how to dance so she doesn't fool herself in front of her date Wes Manning.
In Karl Finds Out Stan's Secret, it turns out that Karl has been spying on the family this whole time and reveals that he had found out Stan's secret in Stan Talks to Gran. Afraid that Karl might reveal Stan's secret, the kids send a message to his mother asking to delete all of the recordings he had made of Stan on his computer, but to everyone's surprise he was spying on them again and reveals to them that he was never going to reveal Stan's secret after he saw how much the kids care about him. Karl and the kids are able to get his mother's phone and delete the message before she reads it and then later reveal to Stan (who had been away at the Doggy Day Spa) that Karl knows his secret but promises that he won't tell anyone.
He's a creepy person and loves spying on others, learning their secrets, and is known for being just plain weird, he was stealing Tyler's draws in attempts to discover what makes girls so attracted to him.
Karl is tall, and has brown hair, which he spikes up in the front. He's also very slim.
Although, she is nearly four times his age, Karl spends a lot of time with Ellen so he can spy on Tyler and Avery. They often have tea together, which they both say "it's not weird!" when it comes up in conversation. Ellen appreciates when Karl calls her beautiful when Bennett does not.
Karl has had a grudge on Avery since they went to science camp together, and she stole his graham crackers. The two are constantly at each others throats, and Karl is always spying on her and Tyler.
Tyler despises Karl just as much as Avery. In The Bone Identity, Karl sees Stan giving Tyler hand signals in the math competition and tries to tell the judge he is cheating. However, Tyler wins and Karl leaves in disgrace.
Not much is known between these two but Karl technically shares a love/hate relationship with Chloe. In Dog Loses Girl, Karl found Chloe and returned her home safely to Ellen, with Chloe not seeming to care about his dark side. In Crimes of the Art, Chloe entered Stan in the art gallery by simply covering his whole fur (save the head) in paint. Karl is outraged when the judge picks Chloe's piece instead of his and he tells his father in shame not to look at the winning art piece. In Don't Karl Us, We'll Karl You, Chloe pretended to be Walter Perkins at Karl's expense, knowing he was Walter Perkins, infuriating him. However, it was all part of a devised plan by Avery and Tyler to remove him from visiting the family home forever. But, eventually, he does return and Karl gets even with Avery and Tyler. Surprisingly Chloe also joins him in his payback scheme by making them wear hats covered in moldy melted cheese, which Karl and Chloe's hats did not have.
Like Avery, Lindsay despises Karl. Their hatred of each other is so far only revealed in The Bone Identity.
Max and Karl went to a school dance with Avery and Lindsay and danced with each other in Avery-body Dance Now.
- The Bone Identity
- Dog Loses Girl
- Crimes of Art
- Avery's Wild Party
- Don't Karl Us, We'll Karl You
- Avery-body Dance Now
- Karl Finds Out Stan's Secret
- Avery Dreams of Kissing Karl
- Stan's New BFF
- Stan Gets Married
- Stan Has Puppies
- Guess Who's Dating Karl
- He sends Ellen some flowers under the name Walter Perkins.
- His dad is up in a space station and his mom is a bodybuilder.
- He lost to Avery in a spelling bee with the word xanthosis.
- He tends to leave his underwear on the bathroom floor.
- He is an only child.
- He often drinks tea with Ellen.
- His name Karl and Walter Perkins last name combined is Karl Perkins. Carl Perkins is the name of musician.
- He doesn't spend much time with his parents.
- He often says weird things only to say, "It's not weird!" right after.
- He and Max said: "It's not weird!" in "Avery-body Dance Now".
- He at first tries revealing Stan's secret in "The Bone Identity". Then he discovers Stan's secret in "Stan Talks to Gran," which reveals that he was aware in "Karl Finds Out Stan's Secret".
- He starts dating Max in "Guess Who's Dating Karl".
- Karl hated Avery when she stole his graham crackers at the Little Smarty Science Camp.
- "You know, you spit a little when you talk."
- "That dog is a math genius!"
- "It's not weird!"