Kapp'n himself is a sailor by nature, referring frequently to his life on the sea and speaking in stereotypical pirate tones. He has also expressed a fondness for women and singing old sea shanties.
According to Katrina, his singing irritates his wife to the extent that he is not allowed to be on the island.
Kapp'n is a sea turtle (Kappa in Japan, hence the name "Kapp'n"). His skin is green and his belly is white. He has a bald spot on the top of his head with triangle hair strands around the edges. He has a green shell on his back that distinguishes him as a turtle.
Kapp'n's clothes vary throughout the games. In Animal Crossing, he wears a simple blue vest. In Wild World, he is more clothed as usual. He wears a blue open coat with white hand collars and a gray shirt underneath, and he wears gray pants with black shoes. He wears a cap on his head, covering his bald spot while still showing his hair. In New Leaf, he is less detailed, wearing a blue white flower patterned t-shirt and grayish-green shorts. He also has red glasses hanging on his left pocket protector. The inside of his mouth is red.
The word "Kappa", from which Kapp'n's name is derived, is the name for a river imp in Japanese folklore. They are mischievous in nature and reptilian in appearance. In one of his shanties, he acknowledges having a boat made of cucumber. This refers to the Kappa's love of cucumbers. His name could also be the sailor pronunciation of 'captain', where letters are missed out in certain words which is how sailors in the past were believed to have talked, saying things like "yar"', "sprat", and "garr", and will sometimes refer to the player as a fish or a sea creature, such as 'scallop', 'Sea Bass', 'Sea Cucumber', and/or 'urchin'.
In Animal Crossing
In Animal Crossing, he is the ferry operator who sails visitors and the player to the island (Animal Island) through the Game Boy Advance cable. During the voyage to the island, he sings a sea shanty, usually about his life on the sea and women.
In Wild World
In Wild World, he drives the black taxi to the town and acts as the introducing character responsible for the gender and appearance of the playable character, as well as the name of the town. This is a role he takes on from Rover. He can sometimes be seen in the The Roost drinking coffee. He will talk about his life at sea upon talking to him and will sometimes seem a bit angry.
In City Folk
In City Folk, he first appears driving the bus to the town, while Rover talks to the playable character determining the gender, the appearance of the character, and the name of the town. He will then appear again driving the bus to the city when going to the Bus Stop. During the journey to the city, he will talk about women, the city and modern day youngsters to male players. If the player is female, he will subtly flirt with them, calling them 'cute' or 'pretty', and say that a 'manly bus-driver is available'. If the player does not respond, he will begin to whistle his sea shanty. He also mentions having a nephew.
He also appears in The Roost, as he did in Wild World, where he will talk about his life in more detail. He will appear there at 15:00 to around 18:00.
In New Leaf
In New Leaf Kapp'n drives a motorized boat and will give the player a ride to the island while singing a little tune along the way. Hearing the song can be skipped by repeatably hitting the 'A' or 'B' buttons. He now has a wife, named Leilani, a daughter named Leila, and his mother Grams living over at the Island's shack. While waiting for the boat to leave on multiplayer, other players cannot join the town.
Kapp'n is seen at the beginning of Dōbutsu no Mori driving Ai to Animal Village in his black taxi, like the one in Wild World. He appears later on in the film during the festival, as a member of the audience listening to K.K. Slider singing.
In Super Smash Bros. Ultimate
Kapp'n appears as an Assist Trophy, based on his appearance in Animal Crossing: City Folk. He will drive his bus towards the blastzone and will take any fighter that he hits.
Even though he acts like an old man, Kapp'n is still just a young sea turtle. He's a little rough around the edges, but he's got a good heart, and he'll sing a sea shanty for anyone who asks. (Even if they don't!)
One of his sea shanties is about cucumbers. In Japanese folklore, cucumbers were thrown into rivers with the names of children and/or families on them. This would spare a family when bathing in a river with a Kappa in it. Children, and sometimes adults, are believed to be one of their favorite foods - cucumbers being their favorite. They would also help humans and not break an oath.
In the middle of his songs, Kapp'n says something to the player. On one of these occasions he makes a claim that he hates squirrels.
Though Kapp'n says, or rather sings, that he loves cucumbers, at the end of his songs, sometimes, he sings that zucchinis give him the spooks, "Zucchini spooks."
If the game is left idle long enough in City Folk while on the bus, Kapp'n will begin to whistle Totakeke's Song, which also appears as K.K. Song. He will also whistle it in New Leaf while on the way to a Club Tortimer island.
In Wild World there is a small figurine in his taxi of him and his boat from Animal Crossing.
In Wild World, if the player takes too long in the taxi at the beginning of the game, the figurine on the dashboard will fall off when getting out.
He is seen on the New Leaf' Japanese Box-art in his boat near the Islands.
In City Folk, Kapp'n will sometimes ask the player (if female) if they will sail away to an island with him. In New Leaf, he and his family live on the paradise island. This might be implying that he followed his dream along with his family.
He has noted that the shell on top of his head is cracked.
Kapp'n has a melody he sings when heading to and away from the island, but in New Leaf, the melody that he sings when going back to the main town is the same melody that he sings to in the original Animal Crossing for the Nintendo GameCube.
In New Leaf, he sometimes sings about writing his love's name in the sand. He ends this by singing "Her name is Leila" before adding a "-ni" at the end. This can be surprising at first, because Leila is a little turtle on the island, presumably his daughter, and Leilani is his wife.