At the end of "Sailor Mouth," when Mama Krabs appears to swear (represented by a honking sound) after stubbing her toe on a rock, she claims that the sound came from Old Man Jenkins, who is driving by in his jalopy, which produces an identical sound. This is the green Old Man Jenkins.
In "My Pretty Seahorse," Old Man Jenkins is among the things eaten by Mystery the Seahorse. Inside her stomach, he says "I don't want to be a burden." He is later spit out, and says "What did I miss?" This is a blue Old Man Jenkins who the name is not applied to in any other episode.
In "The Sponge Who Could Fly" he initially appears as "Farmer Jenkins", whose grain silo is destroyed by SpongeBob's malfunctioning biplane, angering him. He is the main antagonist in this episode, and later, when SpongeBob is able to fly, he reactivates a lighthouse, preventing "Sailor Jenkins" from crashing into it, only for him to turn around and crash into a rock and sink. Towards the end of the episode, "Cannonball Jenkins" launches himself at SpongeBob as he attempts to escape from the mad mob, hitting him and destroying his inflatable pants. In all three of his appearances in this episode, Jenkins says "I told you nothing good would come from city folk and their flying machines!"
In "Friend or Foe," Old Man Jenkins was a friend of Krabs and his mother during the childhood of Krabs and Plankton, and helped them through their time of poverty. He is the first person to try Krabs' and Plankton's burger, and is knocked unconscious by the apparently contaminated patty. His poisoning was the reason that Mr. Krabs and Plankton fell out. There also another fish who looks like similar to Jenkins but has orange skin and hair who being Krab's and Plankton's class teacher at the elementary school. This is the incarnation from "The Sponge Who Could Fly."
In the video game "Creature From the Krusty Krab," Old Man Jenkins appears in the stomach of the Alaskan Bull Worm, and helps SpongeBob collect parts to create a plane. They jump out of the worm together, and soon fight huge Plankton in the plane. They are eventually captured by Plankton, but are saved after Patrick shrinks Plankton to his normal size. This is the version of Old Man Jenkins from "The Sponge Who Could Fly."
In "The Algae's Always Greener," Plankton hides in a ketchup bottle, hoping to be squirted onto a Krabby Patty. However, the bottle is picked up by Old Man Jenkins, who accidentally squirts it towards Mr. Krabs' office.
In "As Seen on TV," he sees SpongeBob on his way to work, and tells him that "I saw you on TV last night!" SpongeBob thinks that he saw him on the Krusty Krab commercial, and begins to believe that he is now a famous celebrity. In reality, the old man saw a commercial for "Bran Flakes", and thought SpongeBob was a cereal box.
In "Fear of a Krabby Patty," he randomly floats by during the montage of SpongeBob working on the order of 10,000 Krabby Patties and gradually losing his mind, saying "Wait, what's going on? Woah. Woah!", thus breaking the fourth wall.
In "Once Bitten," he suggests that everyone might already be zombies, causing them to panic.
In "Rule of Dumb" SpongeBob is seen taking a walker from him to give to king Patrick saying "thank you king Patrick will love your gift." Then the old man replied saying "I hope he needs it. Neptune knows I did," then he fell over.
In "Born to Be Wild," he is a member of the "Mild Ones". An old man resembling the "The Sponge Who Could Fly" version of Old Man Jenkins is also in the gang.
In "Krabs à la Mode", Plankton hides in his soda bottle, and is swallowed when the old man takes a sip. He is freed "four to six hours later", after which Old Man Jenkins attempts to leave the Krusty Krab, but realizes that he has been "locked in again."
In "Roller Cowards," he visits Glove World on his birthday, but is unable to go on the Fiery Fist 'O' Pain due to being in a wheelchair and having a broken arm and leg. SpongeBob and Patrick think that he got injured on the ride, adding to their fear.
In "Money Talks," he is seen eating with Mary and counting how many times he chews.