Role in the series
Knuckles made his first appearance in the episode "Island of the Not-So-Nice". In an attempt to impress the newspaper girl Kaitie, who loves animals, Huey, Dewey, and Louie take Knuckles along without Daisy's knowledge. When Daisy sees them with her beloved pet, she is not too keen on the idea of them taking him. She warns them of how much responsibility it takes to watch Knuckles and reluctantly allows them to take care of him. As the boys go to show off Knuckles to Kaitie, they notice the iguana has gone missing. Knuckles, noticing the doughnuts in Kaitie's bag, stows away on her bike. Huey, Dewey, and Louie chase Knuckles all over town from one location to another until he winds up in a crate full of jars of peanut butter. The crate is being carried and loaded onto a small airplane by a prehistoric caveman named Mungly. The plane takes off and the boys grab onto a loose board connected to the back of the plane as it takes to the sky. However, when they get kidnapped by a mad scientist with a machine that can turn life forms back into their prehistoric ancestors, they find that they might not be able to come through on that promise to Daisy, especially when Knuckles is hit with the Retro-Ray beam and is transformed into a 50-foot dinosaur. Knuckles grows right through the roof of the small hut, roaring out mightily.
The duck triplets are freed from the binds holding them and look on in shock at the now-huge Knuckles, who eats the Retro-Ray and then heads into the ocean back to Duckburg. He starts eating things as the citizens run in terror. Knuckles spitefully plucks a jet that Donald and Daisy were driving out of the sky. He then plucks Daisy out of the jet, tossing Donald and the rest of the plane onto the ground as he grins happily. Knuckles starts to climb up a tall building to get to a giant steel peanut which he thinks is real. Daisy demands to be set down, and he merely drops her onto the side of the building and continues upward, seeing the peanut in view. He is less than pleased to find out the peanut is made of metal, and tosses it down in anger. Huey, Dewey, and Louie arrive with Mungly the caveman aboard a small plane. Knuckles takes a huge swat at the plane, sending it crashing down to the ground as Daisy scolds the boys for allowing this to happen. The boys run into a donut shop and buy a sack full of jelly donuts and load them into a tank. They fire the contents of the sack into Knuckles, who eats them happily and slowly shrinks back down to his original form and size. It seems like the opposite of peanut butter is jelly, so it had the reverse effects on Knuckles. Daisy holds onto her now-normal pet, and Knuckles eats a peanut butter and jelly sandwich.
Knuckles reappears in the episode "Snow Place to Hide". When Donald plans on taking Daisy on a date, he overhears her sweet-talking someone and becomes jealous, only to realize later that it was merely Knuckles whom Daisy was talking to. Daisy tries to reassure Donald that she only has eyes for him, and when she attempts to kiss him, Knuckles steals the kiss with a smirk on his face. However, the smirk does not last when Donald accidentally kisses the iguana, thinking he was Daisy. Knuckles becomes disgusted and wriggles free, falling to the floor.
Knuckles returns in the episode "Transmission: Impossible". While trying their hardest to find something on television that doesn't bore them, Huey, Dewey, and Louie stumble upon a transmission from a Blatismorkian museum security camera and witness the baffling disappearance of a treasured diamond. Knuckles sniffs out the mysterious trail leading them to respected art historian Henry Villanova.
- In his debut episode, when Knuckles is transformed into a 50-foot beast, his appearance and mannerisms are a parody of Godzilla.