Kappa are a species in the Animal Crossing series. They are not a real creature, but rather, a yokai; a creature found in Japanese folklore. Kappa are known for their turtle-like appearances and their bowl-shaped heads filled with water. They are said to live in rivers and act hostile toward humans, but they can be subdued by causing them to bow, which drains the water from their head. They become friendly if fed cucumbers.
The first kappa to appear in Animal Crossing is Kapp'n in Doubutsu no Mori+. Animal Crossing: New Leaf introduces Kapp'n's extended family, including his mother, Grams; his wife, Leilani; and his daughter, Leila. In non-Japanese versions of the series, the kappa are referred to as turtles. This is most likely to avoid confusion, as kappa are largely unknown outside of Japan. However, Kapp'n's English name alludes to his true species.