Old Man Jenkins Jr. is an elderly fish who appears in many episodes, often as a side gag. He makes his debut in "Mermaid Man and Barnacle Boy" and his name is first revealed in the end of "Sailor Mouth." His skinny green form is currently a recurring character in the series.
He has had many different appearances in the series.
In his most recent appearances, he is a bald and wrinkly skinny dark green fish with a light gray beard and eyebrows. He also usually wears blue overalls with two golden snaps along with a brown farmer hat. This is his most notable appearance ever since "High Sea Diving."
Old Man Jenkins' personality depends on which version he is. However, most of the time, he is a quiet, yet adventurous and ambitious elder fish. He dislikes flying machines.
In "The Sponge Who Could Fly," SpongeBob accidentally causes accidents for Old Man Jenkins, causing him to change his profession, from Farmer to Sailor, and then to Cannonball, where he shoots SpongeBob down.
In "High Sea Diving," Old Man Jenkins tricks the Bikini Bottomites into believing he is King Neptune and proclaims himself as ruler of the sea. However, this was brought on because he was trapped up there by his friends on his birthday. He also tried to tell SpongeBob to leave, since he was trying to stop him. After the garbage fell into the city, he attempted to pose as Neptune again while the people were hurt from the fall. When the real King Neptune appears on the scene, he receives his karma since the latter is not impressed with the lies and impersonation Jenkins has done. As punishment for his actions, Neptune zaps the deluded old man with his trident, burning him to a crisp.
His name is a character name used in various episodes as a running gag. His name is first mentioned in "Sailor Mouth." The name was originally applied to the elderly green fish, who appears commonly throughout the series, but in other episodes, the name "Old Man Jenkins" has been used for completely different characters, such as a blueish white fish in a wheelchair and a green fish in overalls. The name is always referred to as elderly fish.
He appears at the end of the episode when Mama Krabs hurts her foot on a small rock and SpongeBob, Patrick, and Mr. Krabs thought she was saying a bad word, but it really turns out to be noise from Old Man Jenkins' jalopy.
When SpongeBob finishes his flying machine, the propeller accidentally cuts a hole in Old Man Jenkins' silo. This makes him angry at SpongeBob and Patrick causing them to run away from him. After that incident, he decided to give up farming and become a sailor instead. He was about to crash into the lighthouse until SpongeBob managed to replace the lightbulb, causing him to turn around, unfortunately he ended up crashing into a large rock and sunk. When SpongeBob was trying to fly away from the angry mob, Old Man Jenkins becomes a stuntman called "Cannonball Jenkins", and he shoots himself right into SpongeBob and punctures his inflated pants.
Old Man Jenkins was Mr. Krabs' neighbor during his childhood. Mr. Krabs and Plankton ask him to try their burger, and when he does, it knocks him out. The event is placed in the newspaper and it caused an argument that ended Mr. Krabs and Plankton’s friendship.
While SpongeBob and Patrick were looking for more information on the main drain he pulls them into his house when he heard them talking about it. He said the main drain is real but unfortunately, he has no idea where it is located.
When SpongeBob finally makes it to the surface of the ocean, he finds Old Man Jenkins at the top with a bunch of junk. He tries to get SpongeBob to believe he is King Neptune and SpongeBob playfully tells him he is Poseidon.
Old Man Jenkins believed he was Poseidon at first, but soon realized it was really SpongeBob. He reveals that he accidentally ended up at the surface by getting pulled up by a bunch of balloons. When they end up getting back down to Bikini Bottom, the Bottomites end up believing that Old Man Jenkins is King Neptune, until the real King Neptune himself arrives and zaps Old Man Jenkins for impersonating him.
After SpongeBob's friends finish the Mermaid Man episode, Old Man Jenkins chases them off for using his outdoor amphitheater. However, he just wanted to play along with them. SpongeBob gladly plays along with him and offers him the role as Mermaid Man, he happily accepts his role and flies off into the sky.
Mr. Krabs has SpongeBob and Patrick work at Old Man Jenkins' farm in order to pay off his grocery bill. They try to finish their assigned tasks and help him prepare for his upcoming barn party, but they end up failing everyone, as well as destroying his barn. After SpongeBob and Patrick do some barn raising, Old Man Jenkins ends up with a brand new barn for his barn party. The party started out slow until a group of Farmer aliens arrived and joined the party. Old Man Jenkins was pleased with SpongeBob and Patrick's help and offered them to come back and visit anytime.
Whenever people run away from Filthy Muck and Little Yuck because of their smell, Old Man Jenkins is the only one to not run, since he cannot smell properly, thus causing him to not smell Filthy Muck and Little Yuck and not be affected by their smell. In the end of the episode, when Patrick reveals to have taken a bath after being kicked out of the Krusty Krab and is in his bath clothes, Old Man Jenkins gets frightened. SpongeBob questions him on this, as he tells him it's because Patrick's bath clothes fell off of him and his butt was being clearly seen by everyone. When everyone realizes this, they all laugh at Patrick's expense.
He comes to the Krusty Krab and disrupts business as normal, and Mr. Krabs tries to get him out. They call for their elders and later get kicked out of the Krusty Krab by them. They then have to go to the Chum Bucket, where Plankton tries to get them to leave but they hit him and tell to respect their elders.
In 2018, Vincent Waller stated on Twitter that as of season 11, the skinny green version of Old Man Jenkins is the only one called by that name. For identification purposes, the production crew now calls the fat version "Old Man Walker" instead. It was revealed in "SpongeBob's Big Birthday Blowout" that the fat version is really named Old Man Walker and is a separate character from Old Man Jenkins.