Barnacle Boy is tall, thin, bald, has a very large nose, puffy ears, wears a sailor hat, a black mask, and a turquoise neckerchief. As an older man, he bears a slight resemblance to Squidward. He also wears dark blue rubber gloves, boots, a red T-shirt, and rubber black shorts. As the younger of the duo, he is more sane and self-aware than Mermaid Man. However, Barnacle Boy is also more cranky. He often calls Mermaid Man an "old coot." He is revealed to be 68 years old in "Mermaid Man and Barnacle Boy V." As his younger self, instead of a black mask, he wears glasses and is much taller. Also, as his younger self, his neckerchief is space-control. His nose is also smaller.
Barnacle Boy possesses powers similar to Mermaid Man, though he lacks the belt powers. Barnacle Boy also has "Sulfur Vision" - a form of heat vision - which Mermaid Man has never been shown to have. Like Mermaid Man, his powers do not work as well as they used to, mostly due to old age.
Despite being a senior citizen, Barnacle Boy is still treated like a child by his mentor, much to his disdain. In "Mermaid Man and Barnacle Boy V," when Mermaid Man orders a Pipsqueak Patty (a very small version of a Krabby Patty intended for children) for Barnacle Boy at the Krusty Krab, they get into an argument, which ultimately results in Barnacle Boy becoming a villain and forming a group called "E.V.I.L." (Every Villain Is Lemons) with Man Ray and the Dirty Bubble. After a protracted fight with Mermaid Man and the "International Justice League of Super Acquaintances" which E.V.I.L. actually wins, he and Mermaid Man patch things up. Barnacle Man (as he prefers to be called) gets a little more respect now.
Mermaid Man and Barnacle Boy are in Rock Bottom when Patrick and Mermaid Man have a soda drinking contest. Patrick ends up winning, but Mermaid Man gets injured and SpongeBob finds help to get him in the invisible boatmobile.
Later, Mermaid Man and Barnacle Boy leave Rock Bottom. At the end of the game, they are at Neptune's Paradise with SpongeBob.
Mermaid Man and Barnacle Boy appear during a new episode being directed by Gill Hammerstein. In it, the duo is falsely accused of destroying the Sand Stadium when it was actually stolen by the Sneaky Hermit. However, when they are sent to Bikini Bottom Jail, the prison warden tells them what is really happening and frees them so they can catch the villain, thus accidentally letting the Dirty Bubble and Man Ray go free.
Mermaid Man and Barnacle Boy go to Goo Lagoon and the Krusty Krab to find clues. When they go to the Chum Bucket, they discover that Man Ray and the Dirty Bubble are using the mayor's child as their captive in an attempt to help the Sneaky Hermit's plans. They reluctantly make a truce with the villains and work together to find the Sneaky Hermit with some help from an expert hunter from Jellyfish Fields.
They manage to track down the hermit and foil his plan of putting Bikini Bottom on his back so he can have a home. When the crisis ends, they return to the Sand Stadium to continue to watch the musical performance.
He has hair growing out the wrinkles on his liver spots.
Barnacle Boy had become a superhero during the 1960s-like era.
He has a case of cauliflower ear, in which the ear becomes swollen and deformed. This condition is commonly seen in elderly people.
In the Russian dub, Barnacle Boy had his name changed several times. Initially, in the first three Mermaid Man and Barnacle Boy-centered episodes, his name was "Очкарик," which roughly translates to "Glasses Boy," then in "Mermaid Man and Barnacle Boy IV," his name was "Прилипала," which roughly translates to "Suction Boy." In "Mermaid Man and Barnacle Boy V," his name was "Юнга," which roughly translates to "Sea Cadet" and in "Mermaid Man & Barnacle Boy VI: The Motion Picture," his name was "Малыш-Ковбой," which roughly translates to "Cowboy Kid."
In the German dub, Barnacle Boy is called "Blaubarschbube," which translates to "bluefish boy." This is not the only instance in SpongeBob where "barnacle" is translated as "Blaubarsch," the other being The Ugly Barnacle (ger. Der hässliche Blaubarsch).
Barnacle Boy's real name is Tim, which is a nod to the first name of his late voice actor Tim Conway.
Mermaid Man's real name, Ernie, shares the same attribute to his own voice actor Ernest Borgnine.
In the Danish dub, he has two names which change during the seasons. In season 1 to 2, he is called "Andeskælsdrengen," which means Barnacle Boy. From season 3 onward, his name was changed to "Klæbedrengen," which means "sticky" or "Glue Boy."