Old Man Jenkins is an elderly fish. His name is a character name used in various episodes as the running gag. The name was originally applied to the elderly green fish in the image to the right, 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 green fish in a wheel chair and a blue fish in overalls. They are always elderly fish. His first name is unknown. He has been voiced by Tom Kenny, Doug Lawrence, and regularly by Dee Bradley Baker. In the episodes "Friend or Foe" and "The Main Drain," he appears except he is taller, has a beard, and is a dark green color. He also doesn't wear glasses.
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.
The reason for so many different versions of Old Man Jenkins has never been explained. However, there could just be different elderly fish with the name Old Man Jenkins, because Jenkins is a common name.
It is revealed in "SpongeGuard on Duty" that Old Man Jenkins is Larry's father. Although, he may just have a vision problem or be confused.