He is voiced by Brian Doyle-Murray also voices The Flying Dutchman.
Captain K'nuckles is not very active and prefers to spend his time in Bubbie's mouth or eating candy at the Candy Barrel (despite him and Flapjack not having enough money or any money at all, and will risk a lot to get 'free eats'). He usually likes to tell stories of his many adventures to Flapjack, and, because of this, the young boy fails to see K'nuckles as the inactive good-for-nothing that he is. K'nuckles is not very bright, as shown in his attempt to do his laundry. Instead of going to the laundromat, he throws his clothes into the ocean and expects them to be thrown back into his arms once they're clean.
He also shows some disgust towards emotional moments, but in the episode Knuckles and his Hilarious Problem it is revealed that after he had too much candy he went into some sort of inebriated state where he confessed to Flapjack that he was the only friend he ever had and that he also cared for Bubbie. After his confession, he began to cry and soon passed out.
Though K'nuckles is shown to neglect Flapjack and their friendship on multiple occasions, he also shows some compassion toward Flapjack and is clearly fond of him as a friend. He might even look at Flapjack as the son he never had. He also seems to have an obsession for Maple Syrup which he also refers to as his friend. He is also illiterate, as seen in many episodes, particularly in "Candy Casanova" where he writes a letter to Candy Wife (which Flapjack reads) using only pictures. Also in Wishing Not So Well, he creates a to-do list using pictures as well.
HEROIC ACT: When K'nuckles tried to rec the storyteller's club he find's out that that group of youngsters kidnapped his old story Telling buddies and that they have been holding them hostage the whole time.
Captain K'nuckles is a human, K'nuckles has a severe case of "whiskers," which causes his entire head to appear blue. The whiskers on his face however, are ironically fake, of which he is greatly ashamed, as seen in "Beard Buddies." He also has scars and numerous tattoos, as evidenced when he is seen shirtless. He is 5'3".
K'nuckles is characterized by his long, orange nose, of which he is very fond of. His hands and legs have been replaced by crude, prosthetic wood, even his rear end is wooden, being a just a plank attached with a belt. Although he eventually reclaimed his real bottom, he lost it in the same episode, "Sittin' Muscle." K'nuckles has an odd waddle when he walks because of this and he makes squeaking noises whenever he moves.
K'nuckles lost one of his hands to a food processor at a young age, he once carved himself a new hand out of wood. Unfortunately, it was a mirror image of the one he needed; he then amputated his working hand and carved a second wooden hand. Fortunately, both prosthetic hands are in excellent working order, allowing K'nuckles to do anything a person with real hands can do (it has been said that he based them off the designs of the best-created mechanical hands ever created, although it is unknown if this is real or he just said this to boost his ego).
K'nuckles constantly wears a red pirate hat and jacket over light brown striped shirt underneath. His hat was given to him by a hatter who, when young K'nuckles asked him if he could have a hat, got one from the harbor ground with a bird nesting in it. Although the hat was covered with bird droppings, K'nuckles was still very proud of having it. He also has also been shown to wear bloomers, as "real men don't wear pants." as he has stated in "That's a Wrap!"
When his irises are seen, it is shown that he has brown eyes. He also has black circles around his eyes. K'nuckles enjoys talking to birds. In the episode "Gone Wishin'," it has shown K'nuckles returning to his original stubble-less human form after making a wish from a mermaid's heart. It is unclear, however, if this is truly his actual normal form.