Carl is a light green fish with mustard yellow fins and pale green lips. He wears big nerdy light blue glasses. He is usually cross-eyed and smiling, and always wears a tight lavender shirt with a purple and pink tie, tight brown pants with a dark brown belt, and black and white shoes. He also has a nametag on his shirt.
In "Selling Out," Carl becomes the new manager of the Krabby O'Monday's shortly after Mr. Krabs retires. He quickly gives Squidward and SpongeBob their uniforms and manuals, and then tells them to work immediately after they are finished. Later, Squidward is upsetting a child with a lousy Krabby O'Monday's birthday song. Because of this, Carl confronts Squidward, and tells him to have sincere service with a smile, or he will be turned over to Human Resources. This causes Squidward to act happy and work faster.
Later, Mr. Krabs returns to the Krabby O'Monday's because he was bored of retirement. He goes to clean a table, which Squidward kindly asks him to do. Mr. Krabs asks Squidward why he is so happy, and Squidward whispers "they're watching us." Mr Krabs gets confused, and says Carl is a "real pain in the hindquarters" causing Carl to get angry. Squidward, afraid to get caught by Carl, tries to show Mr Krabs a message he wrote that says "HELP ME!!!" in his employee handbook, Mr. Krabs reads it out loud, just when Carl shows up. Carl asks what they were doing, and Squidward lies and says he was showing Mr. Krabs article 24, section 3 of his employee handbook to Eugene. Carl believes him, and tells him to "Cut the chatter, pick up a platter. Good job, Squidward." Squidward runs off. Mr. Krabs, confused, asks Carl what he is done to Squidward. Carl slowly backs up into Human Resources and says "the less you know Eugene, the better."
Later, Mr. Krabs discovers that Krabby O'Monday's was using synthetic Krabby Patties. He clogs the machine, and starts scaring the costumers away with the synthetic patties. This causes Carl to get angry and tells him he is in violation with his contract. This makes Mr. Krabs angrier, and he starts destroying the Krabby O'Monday's. Carl then calls up Howard Blandy and tells him "Code red, free thinker." Blandy arrives shortly, but soon, the clogged synthetic machine explodes, causing Carl to be swept away by the synthetic sludge.
He was one of the characters who made a cameo appearance in the episode "Mall Girl Pearl."
His design is based on his voice actor C.H. Greenblatt whose first name is also Carl.