In Avatar, the Navi are an indigenous species that live on Pandora. They are humanoid in appearance and are  tall, having pairs of eyes, ears, arms, legs and feet like humans, as well as a nose, a mouth, and expressions recognizable to humans. The Navi differ from humans in having blue striped skin, pointed and mobile ears, large eyes, catlike noses and tails, and hands each with three fingers and a thumb (hybrid avatars, on the other hand, retain the five-fingered hands of their human DNA). While taller than humans, they have narrower proportions in body frame. Their bones are reinforced with naturally occurring carbon fiber. The Navi also have a distinctive tendril feature protruding from the back of their heads, surrounded by hair (resembling a long plait or queue), feeding directly into the brain. This organ allows them to connect with other organisms, transferring electrochemical signals such as thoughts and memories. In the original script, Cameron refers to these as "Jubilees", although the word is not used in the film and may be changed by the time the novel is published. The Navi were initially conceived to be more alien in appearance. Cameron recalled when one of the main characters, Neytiri, was originally drawn, she had gills and other protuberances. In addition to feline features, the species were redesigned to seem more human so audiences could better relate to them.
The sequel, Avatar: The Way of Water, introduces Navi from the Metkayina tribe with a number of qualities that distinguish them from the blue-skinned Omatikaya clan in Avatar'. The Metkayina have evolved characteristics conducive to an aquatic lifestyle of swimming and diving. These adaptations include green/teal skin, stronger arms, thicker tails, inner eyelids.
According to Cameron, the appearance of the Navi character Neytiri had some specific inspirations and requirements: she was inspired by Raquel Welchs character in Fantastic Voyage and by Vampirella, noting in the latters case, "the fact [Vampirella] didnt exist didnt bother me because we have these quintessential female images in our mind, and in the case of the male mind, theyre grossly distorted. When you see something that reflects your id, it works for you.... Right from the beginning I said, Shes got to have tits, even though that makes no sense because her race, the Navi, arent placental mammals. I designed her costumes based on a taparrabo, a loincloth worn by Mayan Indians." This is somewhat of a non-sequitur because both marsupials (kangaroos, etc.) and monotremes (platypuses, etc.) are non-placental and yet both lactate. This objective of making the Navi as humanlike as possible can also be seen as an explanation as to why they are quadrupedal despite having evolved from common ancestors of the hexapodal lemurs seen in the film.
Cameron has described Avatar as more "science fantasy" than true science fiction and has said that he would explain in the novel for the film why in the fictional universe the Na'vi look like humans.